Sequence amplification with loopable primers

ABSTRACT

The present disclosure relates to the amplification of target nucleic acid sequences. This can be accomplished via the use of various primers. The use of these primers, as described herein, results in nucleic acid structures that can reduce the amplification of nonspecific hybridization events (such as primer dimerization) while allowing the amplification of the target nucleic acid sequences.

RELATED APPLICATION

The present application claims priority to U.S. Provisional ApplicationNo. 60/945,299, filed Jun. 20, 2007, the entirety of which is hereinincorporated by reference.

SEQUENCE LISTING

The present application is being filed along with a Sequence Listing inelectronic format. The Sequence Listing is provided as a file entitledABIOS-073A.TXT, created Jun. 17, 2008, which is 1.53 Kb in size. Theinformation in the electronic format of the Sequence Listing isincorporated herein by reference in its entirety.

FIELD

The invention relates to methods and compositions for amplifying nucleicacid sequences.

INTRODUCTION

Whole genome amplification (WGA) can be a valuable technique foramplification of a genome from minimal or limiting amounts of DNA forsubsequent molecular genetic analysis.

Whole genome amplification can be performed using either conventional ornonconventional PCR amplification methods. Conventional PCR entails theamplification and subsequent detection of specific DNA sequences whichare precisely characterized in length and sequence using nondegenerateprimers, while random, “non-conventional” PCR involves universalamplification of prevailing DNA or amplification of unknown interveningsequences which are not generally defined in length or sequence usingdegenerate primers.

SUMMARY

Some of the present embodiments allow target nucleic acid sequences tobe amplified using at least one loopable primer. In some embodiments,the loopable primer includes a random or degenerate region. In someembodiments, a nucleic acid sequence within the loopable primer includesa universal region and/or a noncomplementary region to reduce thelikelihood of nonspecific hybridization of the primer (such as primerdimers) during subsequent amplification steps.

A loopable primer can include a random region, a first loop formingregion, a universal region, optionally a noncomplementary region, and asecond loop forming region. The first and second loop forming regionsinclude nucleic acid sequences that allow the regions to hybridize toone another. The noncomplementary region is located between the firstand second loop forming regions. The universal region is positionedbetween the two loop forming regions. The noncomplementary region andthe universal region can be configured so that a sequence associatedwith a target sequence that has been amplified by the loopable primer (adouble-extended loopable primer) forms a self-hybridized structureinvolving the noncomplementary region and/or the universal region. Thisself-hybridized structure can allow for the selective amplification oflonger sections of target nucleic acid sequence over shorter sections.The presence of the noncomplementary region can assist in reducingnonspecific binding of various primers throughout the amplificationprocess. The loopable primer can include sequences and structures inaddition to those listed above.

In some aspects, a self-hybridized nucleic acid sequence in a PCRamplification mixture is provided. The self-hybridized nucleic acidsequence includes a first loop forming region, a universal region, anadditional first loop forming region, a random region, a second loopforming region, a sequence that is complementary to the noncomplementaryregion, a sequence that is complementary to the universal priming site,and an additional second loop forming region.

In some embodiments, the present disclosure provides a nucleic acidsequence. The nucleic acid sequence can comprise a 3′ target specificregion, a first loop forming region, a universal region, and a secondloop forming region. The first and second loop forming regions comprisea set of nucleic acid sequences that are configured to hybridize to oneanother. The universal region is located between the first and secondloop forming regions. The universal region is configured so that thenucleic acid sequence can form a self-hybridized structure comprisingthe universal region, the first loop forming region, and the second loopforming region on subsequent amplifications.

In some embodiments, the present disclosure provides a self-hybridizableDNA structure in a PCR amplification mixture. The self-hybridizable DNAstructure can comprise a first loop forming region, a universal regionconnected to the first loop forming region, a second loop forming regionconnected to the universal region, and a first 3′ target specific regionconnected to the second loop forming region. The structure can alsocomprise a sequence that is complementary to a second 3′ target specificregion, wherein the sequence that is complementary to the second 3′target specific region is part of a same nucleic acid strand as thefirst 3′ target specific region. The structure can also comprise asequence that is complementary to the second loop forming region,wherein the sequence that is complementary to the second loop formingregion is connected to the sequence that is complementary to the second3′ target specific region. The structure can also comprise a sequencethat is complementary to the universal region, wherein the a sequencethat is complementary to the universal region is connected to thesequence that is complementary to the second loop forming region. Thestructure can also comprise a sequence that is complementary to thefirst loop forming region, wherein the sequence that is complementary tothe first loop forming region is connected to the sequence that iscomplementary to the universal region.

In some embodiments, the present disclosure provides a method fornucleic acid amplification. The method can comprise allowing a 3′ targetspecific region of a loopable primer to hybridize to a first part of atarget nucleic acid sequence. A loop in the loopable primer isconfigured to allow the 3′ end of the loopable primer to hybridize to afirst part of the target nucleic acid sequence without the remainder ofthe loopable primer annealing to the target nucleic acid sequence. Theloopable primer further comprises a first loop forming region, auniversal region, and a second loop forming region. The first and secondloop forming regions comprise nucleic acid sequences that hybridize toone another. The universal region is located between the first andsecond loop forming regions. The method further comprises extending theloopable primer that is hybridized to the target nucleic acid sequenceto form an extended loopable primer, allowing an additional loopableprimer to hybridize to a complementary part of the target nucleic acidsequence on the extended loopable primer, and extending the loopableprimer to form a double-extended loopable primer.

In some embodiments, the present disclosure provides a nucleic acidsequence comprising a 3′ target specific region, a first loop formingregion, a universal region, a noncomplementary region, and a second loopforming region. The first and second loop forming regions comprise a setof nucleic acid sequences that are configured to hybridize to oneanother. The universal region is located between the first and secondloop forming regions. The noncomplementary region is located between thefirst and second loop forming regions. The universal region isconfigured so that a sequence associated with a target sequence that hasbeen amplified by the nucleic acid sequence can form a self-hybridizedstructure comprising the universal region, the noncomplementary region,the first loop forming region, and the second loop forming region onsubsequent amplifications. The nucleic acid is created by deliberatelyselecting the sequence of the first loop forming region so that ithybridizes to the second loop forming region. The nucleic acid iscreated by deliberately selecting a universal region.

In some aspects, a method for nucleic acid amplification is provided.The method includes allowing a 3′ target specific region of a loopableprimer to hybridize to a first part of a target sequence. A loop in theloopable primer is configured to allow the 3′ target specific region ofthe loopable primer to hybridize to the first part of the targetsequence without the remainder of the loopable primer annealing to thetarget sequence. The loopable primer can include the following: a randomregion, a first loop forming region, a noncomplementary region, and asecond loop forming region. The loopable primer can also include auniversal region. The first and second loop forming regions includenucleic acid sequences that are able to hybridize to one another. Thenoncomplementary region is located between the first and second loopforming regions. The method can further include extending the loopableprimer to form an extended loopable primer, allowing an additionalloopable primer to hybridize to a complementary part of the targetsequence on the extended loopable primer, and extending the additionalloopable primer to form a double-extended loopable primer. Theadditional loopable primer can be the same or different from the firstloopable primer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a depiction of one embodiment of a loopable primer

FIG. 1B is a flow chart depicting an embodiment of a method forselective amplification of a target.

FIG. 1C is a flow chart depicting one embodiment of a method forselective amplification of a target while reducing the risk ofundesirable priming events.

FIG. 2 is a depiction of one embodiment employing loopable primers.

FIG. 3 is a depiction of some embodiments involving amplificationprimers.

FIG. 4 is a depiction of some embodiments in which a double-extendedloopable primer is self-hybridized.

FIG. 5 is a depiction of some embodiments in which a double-extendedloopable primer is self-hybridized.

FIG. 6 is a depiction of some embodiments in which variousdouble-extended loopable primers are self-hybridized.

FIG. 7 is a depiction of some embodiments in which variousdouble-extended loopable primers are self-hybridized.

FIG. 8 is a depiction of various primers, denoting the various subpartsof the primers, such as the first and second loop forming regions, thenoncomplementary region, a universal region and a degenerate or 3′target specific region.

FIG. 9 is an amplification plot showing the relationship between initialstarting material and the number of cycles required to pass a threshold.

FIG. 10 is a depiction of a gel showing the double-extended loopableprimer products produced by some of the present embodiments

FIG. 11 is a depiction of gel demonstrating that amplification of thetarget nucleic acid sequence within the double-extended loopable primerwas achieved, across a variety of variables (including without an Exo Icleaning step).

FIG. 12 is a depiction of a gel demonstrating that amplification wasachieved under a variety of conditions (including with an Exo I cleaningstep).

FIG. 13 is a depiction of a gel demonstrating that amplification wasachieved under a variety of conditions.

FIG. 14 is a depiction of a gel demonstrating that amplification wasachieved under a variety of conditions.

FIG. 15 is a depiction of a gel demonstrating that amplification wasachieved under a variety of conditions.

DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS

The use of loopable primers in the amplification of a target nucleicacid sequence is described herein. In some embodiments, this relates tothe realization that one problem that occurs in target nucleic acidamplification is inadvertent primer dimerization and/or spuriousinternal priming. This can be of concern when random priming regions,degenerate priming regions, universal priming regions, or somecombination thereof are used, especially in multiplexed embodiments. Insuch embodiments, large numbers of various primer sequences are used,which increases the likelihood that undesired priming (e.g., such asprimer dimers) will occur.

In some embodiments, this issue has been addressed through the use ofloopable primers that include a universal region and optionally anoncomplementary region within the loop of the loopable primer. In someembodiments, this results in the more efficient amplification of targetnucleic acid sequences. Some embodiments of the technique can alsoreduce the effect of spurious internal priming. In some embodiments, thenoncomplementary region within the looped section of the primer canreduce the likelihood that inadvertent primer dimerization will occur.In some embodiments, the target nucleic acid sequence is genomic DNA. Insome embodiments, the method can be applied to allow for more efficientamplification of large amounts of gDNA, such as for whole genomeamplification. The above as well as additional embodiments are describedin greater detail following the definition and alternative embodimentssection provided below.

SOME DEFINITIONS AND ALTERNATIVE EMBODIMENTS

As used herein, the term “target nucleic acid sequence” refers to apolynucleotide sequence that is sought to be detected in a sample. Thetarget nucleic acid sequence can be obtained from any source and caninclude any number of different compositional components. For example,the target can be nucleic acid (e.g. DNA or RNA), transfer RNA, siRNA,and can include nucleic acid analogs or other nucleic acid mimics. Thetarget can be methylated, non-methylated, or both. The target can bebisulfite-treated and non-methylated cytosines converted to uracil.Further, it will be appreciated that “target nucleic acid sequence” canrefer to the target nucleic acid sequence itself, as well as surrogatesthereof, for example amplification products, and native sequences. Insome embodiments, the target nucleic acid sequence is a miRNA molecule.In some embodiments, the target nucleic acid sequence lacks a poly-Atail. In some embodiments, the target nucleic acid sequence is a shortDNA molecule derived from a degraded source, such as can be found in,for example but not limited to, forensics samples (see for exampleButler, 2001, Forensic DNA Typing: Biology and Technology Behind STRMarkers). In some embodiments, the target nucleic acid sequences of thepresent teachings can be present or derived from any of a number ofsources, including without limitation, viruses, prokaryotes, eukaryotes,for example but not limited to plants, fungi, and animals. These sourcescan include, but are not limited to, whole blood, a tissue biopsy,lymph, bone marrow, amniotic fluid, hair, skin, semen, biowarfareagents, anal secretions, vaginal secretions, perspiration, saliva,buccal swabs, various environmental samples (for example, agricultural,water, and soil samples), research samples generally, purified samplesgenerally, cultured cells, and lysed cells.

It will be appreciated that target nucleic acid sequences can beisolated or obtained from samples using any of a variety of proceduresknown in the art, for example the Applied Biosystems ABI Prism™ 6100Nucleic Acid PrepStation, and the ABI Prism™ 6700 Automated Nucleic AcidWorkstation, Boom et al., U.S. Pat. No. 5,234,809, mirVana RNA isolationkit (Ambion), etc. It will be appreciated that target nucleic acidsequences can be cut or sheared prior to analysis, including the use ofsuch procedures as mechanical force, sonication, restrictionendonuclease cleavage, or any method known in the art. Cleaving can bedone specifically or non-specifically. In general, the target nucleicacid sequences of the present teachings will be single stranded, thoughin some embodiments the target nucleic acid sequence can be doublestranded, and a single strand can result from denaturation. In someembodiments, the target nucleic acid sequence is genomic DNA.

As will be appreciated by one of skill in the art, the term “targetnucleic acid sequence” can have different meanings at different stepsthroughout the method. For example, in an initial sample, there can be atarget nucleic acid sequence that is 2 kb in length. When this isamplified by the loopable primer to form a double-extended loopableprimer, part of the target nucleic acid sequence can be contained withinthe double-extended loopable primer; however, not all of the targetnucleic acid sequence need be contained within the double-extendedloopable primer. Regardless of this, the section of the target nucleicacid sequence that is amplified can still be referred to as the “targetnucleic acid sequence” (in part because it will still indicate thepresence or absence of the large target nucleic acid sequence of whichit is a part). Similarly, when the section of the insert section, whichcontains the target nucleic acid sequence, is amplified by the insertamplification primers it can also be described as amplifying the “targetnucleic acid sequence.” One of skill in the art will appreciate that,likely, the length of the target nucleic acid sequence will decrease asthe sequence is processed further. If necessary, each target nucleicacid sequence in each step can be specifically designated as an “initialtarget nucleic acid sequence,” a “double-extended loopable primer targetnucleic acid sequence”, and a “insert section target nucleic acidsequence.” Additionally, one of skill in the art will appreciate thatthe sequence that one is interested in determining if present in asample can be a separate sequence from a target nucleic acid sequencethat is amplified. For example, the sequences can be in linkagedisequilibrium or from a different part of a gene or stretch of nucleicacids. Such sequences can be termed “inquiry target nucleic acidsequences.”

As used herein, the term “loopable primer” refers to a moleculecomprising a 3′ target specific portion, a stem (comprising a first loopforming region and a second loop forming region), and a loop portion.Illustrative loopable primers are depicted in FIG. 1A and elsewhere inthe present teachings. It will be appreciated that the loopable primerscan be comprised of ribonucleotides, deoxynucleotides, modifiedribonucleotides, modified deoxyribonucleotides, modifiedphosphate-sugar-backbone oligonucleotides, nucleotide analogs, orcombinations thereof. For some illustrative teachings of variousnucleotide analogs etc, see Fasman, 1989, Practical Handbook ofBiochemistry and Molecular Biology, pp. 385-394, CRC Press, Boca Raton,Fla., Loakes, N.A.R. 2001, vol 29:2437-2447, and Pellestor et al., Int JMol. Med. 2004 April; 13(4):521-5), references cited therein, and recentarticles citing these reviews. It will be appreciated that the selectionof the loopable primers to query a given target nucleic acid sequence,and the selection of which collection of target nucleic acid sequencesequences to query in a given reaction with which collection of loopableprimers, will involve procedures generally known in the art, and caninvolve the use of algorithms to select for those sequences with minimalsecondary and tertiary structure, those targets with minimal sequenceredundancy with other regions of the genome, those target regions withdesirable thermodynamic characteristics, and other parameters desirablefor the context at hand. In some embodiments, the loop section includesone or more additional nucleic acids that serve a desired function. Insome embodiments, a universal primer is included within the loop. Insome embodiments, a noncomplementary region or sequence is includedwithin the loop. In some embodiments, an identifying portion is includedwithin the loop.

As will be appreciated by one of skill in the art, even though a primeris “loopable” it may not always be in its looped form. For example, athigh temperatures or salt conditions, the two loop forming regions canseparate from one another. However, even in situations where theloopable primer is not actually looped, it can still be referred to as a“loopable primer.” Thus, the term “loopable primer” does not requirethat the primer actually be in the looped configuration.

As used herein, the term “3′ target-specific portion” refers to a singlestranded portion of a loopable primer that is complementary to at leasta portion of a target nucleic acid sequence. The 3′ target-specificportion is located downstream from the stem of the loopable primer.Generally, the 3′ target-specific portion is between 4 and 15nucleotides long and can be between 6 and 12 nucleotides in length. Insome embodiments, the 3′ target-specific portion is 7 nucleotides long.It will be appreciated that routine experimentation can be used tooptimize length, and that 3′ target-specific portions that are longerthan 8 nucleotides or shorter than 6 nucleotides are also contemplatedby the present teachings. In some embodiments, modified bases such asLNA can be used in the 3′ target specific portion to increase thestability, for example by increasing the Tm of the loopable primer (seefor example Petersen et al., Trends in Biochemistry (2003), 21:2:74-81).In some embodiments, universal bases can be used in the 3′ targetspecific portion, for example to allow for smaller libraries of loopableprimers. Universal bases can also be used in the 3′ target specificportion to allow for the detection of unknown targets (e.g., targets forwhich specific binding sequences are not known). For some descriptionsof universal bases, see for example Loakes et al., Nucleic AcidsResearch, 2001, Volume 29, No. 12, 2437-2447. In some embodiments,modifications including but not limited to LNAs and universal bases canimprove reverse transcription specificity and potentially enhancedetection specificity.

In some embodiments, the 3′ target-specific region includes or is adegenerate region, a random region, a specific region, or a knownsequence. In some embodiments, the 3′ target specific region includes acombination of these regions. In some embodiments, the 3′ targetspecific regions have a Tm of between about 10° C. and 50° C. In someembodiments, a 15-mer has a Tm of less than about 60° C.

The term “degenerate primer” when used herein refers to a mixture ofsimilar primers with differing bases at the varying positions(Mitsuhashi M, J Clin Lab Anal, 10(5):285 93 (1996); von Eggeling etal., Cell Mol Biol, 41(5):653 70 (1995); (Zhang et al., Proc. Natl.Acad. Sci. USA, 89:5847 5851 (1992); Telenius et al., Genomics,13(3):718 25 (1992)). Such primers can include inosine as inosine isable to base pair with adenosine, cytosine, guanine or thymidine.Degenerate primers allow annealing to and amplification of a variety oftarget sequences that can be related. Degenerate primers that anneal totarget DNA can function as a priming site for further amplification. Adegenerate region is a region of a primer that varies, while the rest ofthe primer can remain the same. Degenerate primers (or regions) denotemore than one primer and can be random. A random primer (or regions)denotes that the sequence is not selected, and it can be degenerate. Insome embodiments, the 3′ target specific regions have a Tm of betweenabout 10° C. and 50° C. In some embodiments, a 15-mer has a Tm of lessthan about 60° C.

A “specific region” (in contrast to a “3′ target specific region” whichis a broader genus) is able to bind to a specific genomic sequenceoccurring in the human genome with a specific frequency. In someembodiments, this frequency is between about 0.01% and 2.0%, such as,for example, between about 0.05% and 0.1% or between about 0.1% and0.5%. In some embodiments, the length of the “specific region” of aprimer depends mainly on the averaged lengths of the predicted PCRproducts based on bioinformatic calculations. The definition includes,without limitation, a “specific region” of between about 4 and 12 basesin length. In more particular embodiments, the length of the 3′ specificregion can, for example, be between about 4 and 20 bases, or betweenabout 8 and 15 bases. Specific regions having a Tm of between about 10°C. and 60° C. are included within the definition. The term, “specificprimer,” when used herein refers to a primer of specified sequence. Anexample of a specific region would be a region for priming for theamplification of a STR locus.

The term “random region” as used herein refers to a region of anoligonucleotide primer that is able to anneal to unspecified sites in agroup of target sequences, such as in a genome. The “random region”facilitates binding of the primer to target DNA and binding of thepolymerase enzyme used in PCR amplification to the duplex formed betweenthe primer and target DNA. The random region nucleotides can bedegenerate or non-specific, promiscuous nucleobases or nucleobaseanalogs. The length of the “random region” of the oligonucleotideprimer, among other things, depends on the length of the specificregion. In certain embodiments, without limitation, the “random region”is between about 2 and 15 bases in length, between about 4 and 12 basesin length or between about 4 and 6 bases in length.

In some embodiments, the 3′ target-specific portion comprises both aspecific region and a random region or degenerate region. In otherembodiments, the 3′ target-specific portion includes a specific region,a random region or a degenerate region. In other embodiments, the 3′target specific region of the loopable primer only includes a specificregion, a random region, or a degenerate region.

In some embodiment, the specific and random regions combined will beabout 9 bases in length, e.g., if the specific region has 4 bases, therandom region will have 5 bases.

As used herein, the term “stem” refers to the double stranded region ofa loopable primer that is between the 3′ target-specific portion and theloop. Generally, the stem is between 6 and 20 nucleotides long (that is,6-20 complementary pairs of nucleotides, for a total of 12-40 distinctnucleotides). In some embodiments, the stem is 8-14 nucleotides long.Those in the art will appreciate that stems shorter than 6 nucleotidesand longer than 20 nucleotides can be identified in the course ofroutine methodology and without undue experimentation, and that suchshorter and longer stems are contemplated by the present teachings. Insome embodiments, the stem can comprise an identifying portion. In someembodiments, the stem includes a first loop forming region and a secondloop forming region, which, when hybridized together, create the stemstructure.

As used herein, the term “loop” in reference to the loopable primerrefers to a region of the loopable primer that is located between thetwo complementary strands of the stem, e.g., as depicted in FIG. 1A.Typically, the loop includes single stranded nucleotides, though othermoieties modified DNA or RNA, Carbon spacers such as C18, and/or PEG(polyethylene glycol) can also be included in the loop. Generally, theloop is between 4 and 20 nucleotides long. In some embodiments, the loopis between 14 and 18 nucleotides long. In some embodiments, the loop is16 nucleotides long. Those in the art will appreciate that loops shorterthat 4 nucleotides and longer than 20 nucleotides can be identified inthe course of routine methodology and without undue experimentation, andthat such shorter and longer loops are contemplated by the presentteachings. In some embodiments, the loop can comprise an identifyingportion. As will be appreciated by one of skill in the art, the sectionof the nucleic acid sequence that forms the loop need not always be in aloop.

As used herein, the “first loop forming region” refers to a nucleic acidsequence which includes a sequence that is capable of hybridizing to asecond loop forming region in the same loopable primer, viaintramolecular hybridization. This hybridization can form the loopedsection of the loopable primer. As will be appreciated by one of skillin the art, the length of the first loop forming region can vary. Insome embodiments, the first loop forming region is between 5 and 20nucleic acids long. In some embodiments, the stem length is long enoughto form a stable looped structure at the annealing temperature. In someembodiments, melting point of the first loop forming region hybridizedto the second loop forming region is about 10° C. to 20° C. higher thanthe annealing temperature of the 3′ target specific region. For example,in embodiments in which annealing is performed at 35° C., an 8 base stemcan be used that has a 55° C. Tm.

As will be appreciated by one of skill in the art, in some embodiments,the melting point is high enough so that the loopable primer is in aloop form during hybridization to the target sequence. In someembodiments, the melting point is low enough so that the loopable primercan linearize during various extension steps. In some embodiments, thefirst and second loop forming regions, when hybridized together, have aTm that is at least above the former temperature and at least at orbelow the latter temperature. In some embodiments, the melting point islow enough to allow the universal primer to anneal to the template. Insome embodiments, the Tm is below 70° C.

As used herein, the “second loop forming region” refers to a nucleicacid sequence that includes a sequence that is configured for andtherefore capable of hybridizing to a first loop forming region in thesame nucleic acid segment, via intramolecular hybridization underparticular conditions.

As used herein, the “noncomplementary region” refers to nucleic acidsequence in a loopable primer or product thereof. In some embodiments,the noncomplementary region is located between the first and second loopforming regions. In some embodiments, the noncomplementary region is asequence that is present in at least some of the various primers orsequences in a reaction mixture. In some embodiments, the sequence iscommon in all or less than all of the primers used, for example 100,100-99, 99-95, 95-90, 90-80, 80-70, 70-60, 60-50, 50-40, 40-30, 30-20,20-10, 10-5, 5-1, 1% or less. Thus, in some embodiments, the primers forthe target amplification all contain the same noncomplementary sequence.In some embodiments, the primers in subsequent steps (or a percent asnoted above) also have the same noncomplementary region. As will beappreciated by one of skill in the art, the presence of similarsequences across various primers will reduce the likelihood that primerdimerization will occur (as the primers will be less likely to hybridizeto one another). In some embodiments, the noncomplementary region isnoncomplementary with respect to sequences in the target nucleic acidsequence. This embodiment is described in more detail below. In someembodiments, the noncomplementary region is both present in variousprimers (thereby reducing primer dimerization) and noncomplementary tosequences in the target sequences (e.g., a relatively long series ofthymines)

The presence of the noncomplementary sequence need not absolutelyprevent the occurrence of primer dimerization or other forms ofnonspecific hybridization in every situation. In some embodiments, thepresence of the noncomplementary region reduces the likelihood of theseundesired forms of hybridization from occurring. In some embodiments,any decrease is sufficient, for example, less than 100% of the dimersthat would have occurred without the noncomplementary region, e.g.,100-99, 99-98, 98-,95, 95-90, 90-80, 80-70, 70-60, 60-50, 50-40, 40-30,30-20, 20-10, 10-5, 5-1, or less of the original primer dimers willoccur when the noncomplementary region is present in the loopableprimer. In some embodiments, the presence of the noncomplementary regiondecreases likelihood of nonspecific amplification or amplification ofundesirably small sections of target nucleic acid sequence.Additionally, while the noncomplementary sequence can be the same in allof the primers or loopable primers used, it need not be the same. Forexample, in some embodiments, the noncomplementary regions, while nothybridizing, are not the same sequences (e.g., TTTT vs. CCCC). In otherembodiments, the noncomplementary regions are similar, but notidentical, (e.g., TTTT vs. TTTC). In other embodiments, thenoncomplementary regions are completely different types or sequences ofnucleic acids; however, they will still reduce the likelihood of variousforms of nonspecific hybridization. As will be appreciated by one ofskill in the art, the length of the noncomplementary region can vary andthe length required can depend on the various reaction conditions andthe sequences present in the target sample, issues that can readily bedetermined by one of skill in the art.

In some embodiments, the noncomplementary region is effective atreducing the nonspecific hybridization of an amplification primer. Theamplification primer can have a region that hybridizes to thenoncomplementary region (as well as a region that can hybridize to theuniversal region). Thus, the amplification primer can be more specificfor the double-extended loopable primer products rather than othernonspecific priming events that could occur if the amplification primeronly contained a universal region. Thus, in some embodiments, thepresence of the noncomplementary region in the loopable primer canassist in reducing subsequent nonspecific amplification.

In some embodiments, the noncomplementary region is at least 3-15nucleic acids in length. In some embodiments, the noncomplementaryregion comprises a series of thymine nucleic acids. In some embodiments,the noncomplementary region is 8-12 thymines. In some embodiments, thenoncomplementary region only includes 3, 4, 5, 6, 7, 8, 9, 10, 11, 12,13, 14, 15, 16, 17, 18, 19, or 20 thymines (T) or adenines (A) orsimilar nucleic acids (such as artificial nucleic acids).

As will be appreciated by one of skill in the art, while the term“noncomplementary” can denote that the sequence does not significantlyor functionally complement another sequence in a mixture, there will besequences that can hybridize to the noncomplementary region. Forexample, in a double-extended loopable primer (FIG. 3) there is both thenoncomplementary region 30 and the complement to the noncomplementaryregion 30′. Additionally, as noted above, in some embodiments, theamplification primer can also include a sequence that can hybridize tothe noncomplementary region.

The term “does not effectively hybridize” denotes that the amount ofhybridization that occurs is sufficient so that a significant reductionin primer dimerization or other forms of nonspecific hybridizationoccurs. As will be appreciated by one of skill in the art.

As used herein, the “target binding site” refers to a nucleic acidsequence, in the target nucleic acid sequence, where the 3′target-specific portion of the loopable primer can or is configured tohybridize to. As will be appreciated by one of skill in the art, thissection can be part of the target nucleic acid sequence and cantherefore be gDNA or other nucleic acid sequences.

As used herein, the “extended loopable primer” refers to a nucleic acidsequence that has been extended from a loopable primer hybridized to atarget binding site. The extended loopable primer can include theloopable primer, along with a sequence that is effectively complementaryto a sequence that is contained within the target sequence (in additionto the target binding sequence). In some embodiments, the extendedportion of the extended loopable primer is at least 100 nucleic acids inlength. In some embodiments, the extended portion is at least 200nucleic acids in length. In some embodiments, the extended portion isnot more than 10 kb in length. However, in other embodiments, otherlengths are contemplated. As will be appreciated by one of skill in theart, the “extended loopable primer” will include a loopable primer;however, it will not need to serve as a primer itself. In someembodiments the loopable primer portion of it is still looped, althoughthis is not required.

As used herein, the “loopable primer complement” refers to a nucleicacid sequence that is the complement of the loopable primer (of course,the loopable primer complement need not be 100% complementary, as the 3′target specific regions can include degenerate or random regions). Aswill be appreciated by one of skill in the art, the sequence of theloopable primer complement can still form a looped primer itself.Additionally, any universal region and/or noncomplementary region in theloopable primer complement will be complementary to the relevant sectionin the loopable primer. An example of a loopable primer complement canbe found in FIG. 3, on the right hand side of sequence 4, includingsections 10, 20′, 30′, 10′, and 52. However, as noted above, a loopableprimer complement need not have a complementary 3′ target specificregion to the 3′ target specific region in the loopable primer (as thesecan be from different initial loopable primers.

As used herein, the “universal region complement” refers to a nucleicacid sequence that is the complement of the universal region.

The term “double extended looped primer” refers to a nucleic acidsequence that has been formed by extending a loopable primer that ishybridized to an extended loopable primer. In other words, the nucleicacid sequence has been extended twice via loopable primers. In someembodiments, the term “double extended looped primer” simply means thatthere is a nucleic acid sequence that includes a loopable primer, atarget sequence, and a loopable primer complement; the method by whichit is made is not relevant. In some embodiments, the term “doubleextended looped primer” simply means that there is a nucleic acidsequence that includes a universal region, a target sequence, and auniversal region complement; the method by which it is made is notrelevant. As will be appreciated by one of skill in the art, the“double-extended loopable primer” can include a loopable primer and aloopable primer complement; however, it does not necessarily to serve asa primer itself. In some embodiments the loopable primer portion of itis still looped, although this is not required.

The “amplification primer” primer need not be looped. An example of sucha primer is depicted in FIG. 3, as 60. In some embodiments, theamplification primer is a linear primer. In some embodiments, theamplification primer is not complementary to the loopable primer. Insome embodiments, the amplification primer has at least some of the samesequence as the loopable primer. In some embodiments, the amplificationprimer includes a sequence that is the same as the universal region. Insome embodiments, the amplification primer includes a sequence that isthe same as the noncomplementary region. In some embodiments, theamplification primer includes a sequence that is the same as theuniversal region. In some embodiments the amplification primer furtherincludes a sequence that is the same as the second loop forming region.In some embodiments, the amplification primer includes the second loopforming region, the universal region, and (optionally) thenoncomplementary region. As will be appreciated by one of skill in theart, the sequences need not be identical in all embodiments, assequences that still selectively hybridize to the desired location canbe employed as well. In some embodiments, the amplification primer isbetween 10-40 nucleotides long, such as a 30-mer. In some embodimentsthe amplification primer is 14 nucleotides long. In some embodiments,the amplification primer includes a “universal reverse primer,” whichindicates that the sequence of the reverse primer can be used in aplurality of different reactions querying different target nucleic acidsequences, but that the amplification primer nonetheless can be the samesequence. In some embodiments, the amplification primer includes a tailregion that is not complementary to the sequence that the rest of theprimer hybridizes to.

The term “insert section” or “insert target” or “capture section” refersto the section from one 3′ target specific region to a second 3′ targetspecific region, as shown in FIG. 4. In some embodiments, the insertsection includes the 3′ target specific region as well; thus, the insertsection includes 52 and 50 in FIG. 4, and is defined between the firstloop forming region 10 and the second loop forming region 10′. Theinsert section 9 can include a significant portion of target nucleicacid sequence, as shown in FIG. 4, which can then be amplified.Alternatively, the insert section can contain an insignificant amount oftarget DNA 51 (such as when primer dimers occur or overly frequentpriming occurs), such an embodiment is shown in FIG. 5. In someembodiments, the insignificant amount of DNA 51 will be no DNA, as such,the insert section is only 50 connected to 52. In other embodiments, asmall amount of the target nucleic acid sequence is included 51. In someembodiments, the insert section for the double-extended loopable primerto be amplified is between 200 bp and 10 kb nucleic acids in length. Insome embodiments, the insert section for the double-extended loopableprimer to be amplified is between 100 bp and 20 kb nucleotides inlength.

As will be appreciated by one of skill in the art, in some embodiments,the insert section 9 can be looped, such as by the hybridization of theuniversal region and the universal region complement in adouble-extended primer 8, as shown in FIG. 4, (e.g., the loop formed bythe self-hybridization of the double-extended linear primer). However,in other embodiments, the insert section is not actually looped duringvarious amplification steps (although they will be looped for theshorter insert sections, such as primer dimers, that are not to beamplified). As described in more detail below, even when not part of alooped structure, the length of the insert section or target section canstill influence the amplification of the section. For example, shorterlength insert sections will result in closer to zero order reactionkinetics between the universal region and its complement, while longerinsert sections will increase the distance between the universal regionand its complement, resulting in slower reaction kinetics. Thus, doubleextended loopable primers need not be looped in order to allow forselective amplification of longer insert sections over shorter insertsections. As will be appreciated by one of skill in the art, one cancharacterize the insert section as including some of the loopable primersequence. Unless otherwise stated, “insert section” will include theregion to which the loopable primer initially binds. Thus, a doubleextended loopable primer that is only a primer dimer, even if itincludes nothing more than the random region of the loopable primer, canstill be characterized as “having” some part of an insert section thatis shorter than another double extended loopable primer. That is, an“insert section” does not have to include any target (or foreign)nucleic acid sequence and can simply be one or two random regions fromthe loopable primers.

The “capture stem” or “insert stem” denotes the section of thedouble-extended loopable primer that is self-hybridized. As will beappreciated by one of skill in the art, when the double extendedloopable primer is simply a primer dimer, without any additional targetnucleic acid sequence, the insert section will comprise the originalloopable primer sequences. As the structure can still be looped, therecan still be unpaired nucleotides within the loop (although there neednot be). Such primer dimer formations can be characterized as having “noforeign insert section”, as they contain no additional sequence, apartfrom the starting primers; however, as they will still include the 3′target specific regions, there can still be a sequence within the insertsection, even though none of it is foreign.

The term “insert amplification primer” refers to a primer that can beused to amplify an insert section. Generally, these primers arecomplementary to some section of the target nucleic acid sequence thatis within the double-extended loopable primer. In some embodiments, theinsert amplification primers are specific primers with known or knowablesequences. Thus, in some embodiments, numerous insert amplificationprimers will be employed as the specific sequence that has beenamplified may not be known. In some embodiments, two or more insertamplification primers are used to amplify the insert sections. In someembodiments, each insert amplification primer (or paired set thereof)will be combined with the double-extended loopable primer in a separatereaction chamber (thus the amplified double-extended loopable primerwill be divided among numerous reaction chambers). In other embodiments,the numerous insert amplification primers and the amplification reactionare performed in a single reaction chamber or are combined in somemanner. In some embodiments, the insert amplification primers aredegenerate primers. In some embodiments, the insert amplificationprimers are relatively short to allow for ease of amplification. In someembodiments, the insert amplification primers include universal bases.

The term “intramolecular hybridization” refers to an event or state inwhich a nucleic acid strand is hybridized to itself. This can includeboth the hybridization event that is present in the looped primer, aswell as the hybridization event that occurs between the two ends of adouble extended looped primer via the universal region and the universalregion complement.

The terms “self-hybridizing” or “self-hybridized” refer to an event orstate in which a portion of a nucleic acid strand is hybridized toanother portion of itself. While the loopable primers areself-hybridizing, in general, the term is reserved for the effectivehybridization of the universal region of the loopable primer to at leasta portion of the universal region complement (which can be within aloopable primer complement) in a double extended loopable primer, e.g.,as shown in FIG. 4 configuration 8. For example the universal region canbe hybridized to the universal region complement.

The term “large enough to allow amplification” in reference to theinsert section (or capture section) denotes that, relative to otherspecies of sequences in the reaction mixture, the larger size of theinsert section of the described species allows for greater or moreefficient amplification. If an insert section has a “significant portionof target DNA” it will be large enough to allow amplification. In someembodiments, the insert section is between 200 bp and 10 kb or morenucleic acids in length. In some embodiments, the relative prevention ofamplification is between a primer dimer (which comprises only thesequence of the loopable primer, e.g., a primer dimer) and a doubleextended loopable primer that includes at least one nucleotide inaddition to the loopable primer.

The term “short enough to reduce the likelihood that amplification willoccur” in reference to the insert section denotes that, relative toother species of sequences in the reaction mixture, the smaller size ofthe insert of the described species results in less and/or lessefficient amplification compared to another species in the reactionmixture. If an insert has “an insignificant amount of target DNA” it issmall enough to prevent or reduce the likelihood of amplification of DNAwithin the insert. In some embodiments, an insert that is short enoughto reduce the likelihood that amplification will occur is between 1 and200 nucleotides in length. As will be appreciated by one of skill in theart, as the loopable primer and primer complement can include a 3′target specific region some amount of a target nucleic acid sequence canbe present, even in situations where simple primer dimerization hasoccurred. In some embodiments, these two terms are defined relative toone another. As will be appreciated by one of skill in the art in lightof the present disclosure, in some embodiments, the size of the insertsection (or insert section) is being used to preferentially reduce theamplification of smaller amplified regions of the target nucleic acidsequence compared to larger target nucleic acid sequences. Thus, in someembodiments, the “prevention” or “reduction” of the amplification of afirst double-extended loopable primer over a second double-extendedloopable primer results from the fact that the first has a shorterinsert section compared to the second. In some embodiments, anydifference in size of the insert section can result in the desired“reduction” or selective amplification, for example, the first doubleextended can be 99-90, 90-80, 80-70, 70-60, 60-50, 50-40, 40-30, 30-20,20-10, 10-5, 5-1, 1-0.1, 0.1-0.001% or less the size of the insertsection in the second double-extended loopable primer. In someembodiments, the prevention or reduction is specific to the preventionof the amplification of primer dimers. In some embodiments, the relativeprevention is between designated larger and smaller inserts. In someembodiments, the relative prevention or reduction in likelihood is incomparison to the same sequence as the insert sequence, except that thesequence is not looped (e.g., same insert sections sequence, but no orinsignificant amounts of the stem forming region).

As will be appreciated by one of skill in the art, in embodiments inwhich one is amplifying within a self-hybridized structure, at largeenough lengths, the amplification in the insert section does not changesignificantly upon increasing the length of the nucleic acid sequence inthe insert section. However, these sequences can still be preferentiallyamplified over double-extended loopable primers having shorter lengthsof insert sections. As noted below, in some embodiments, insert sectionsof at least 100 bp are generally used in order to have amplification inthe loop. In embodiments in which SNP genotyping and gene dosage RT-PCRare employed, the length of the loops can be 100 bp or longer, in orderto allow spacing for two primers and probes (e.g., TAQMAN® probes). Forsome embodiments, such as capillary electrophoresis for sequencingapplications, the insert sections can be 500 bp or longer. Insertsections of at least 500 bp can result in very efficient amplificationin the loop. If longer loops are desired, the annealing time and/orextension time can be increased during PCR. In embodiments in which aself-hybridized structure is not formed for the longer double-extendedloopable primer, then there need be no minimal size, as long as it islonger than the other double-extended loopable primer that the longdouble extended loopable primer is to be amplified over.

As used herein, the term “identifying portion” refers to a moiety ormoieties that can be used to identify a particular loopable primerspecies, and can refer to a variety of distinguishable moietiesincluding zipcodes, a known number of nucleobases, and combinationsthereof. In some embodiments, an identifying portion, or an identifyingportion complement, can hybridize to a detector probe, thereby allowingdetection of a target nucleic acid sequence in a decoding reaction. Theterms “identifying portion complement” typically refers to at least oneoligonucleotide that comprises at least one sequence of nucleobases thatare at least substantially complementary to and hybridize with theircorresponding identifying portion. In some embodiments, identifyingportion complements serve as capture moieties for attaching at least oneidentifier portion and target nucleic acid sequence to at least onesubstrate; serve as “pull-out” sequences for bulk separation procedures;or both as capture moieties and as pull-out sequences (see for exampleO'Neil, et al., U.S. Pat. Nos. 6,638,760, 6,514,699, 6,146,511, and6,124,092).

Typically, identifying portions and their corresponding identifyingportion complements are selected to minimize: internal,self-hybridization; cross-hybridization with different identifyingportion species, nucleotide sequences in a reaction composition,including but not limited to gDNA, different species of identifyingportion complements, or target-specific portions of probes, and thelike; but should be amenable to facile hybridization between theidentifying portion and its corresponding identifying portioncomplement. Identifying portion sequences and identifying portioncomplement sequences can be selected by any suitable method, for examplebut not limited to, computer algorithms such as described in PCTPublication Nos. WO 96/12014 and WO 96/41011 and in European PublicationNo. EP 799,897; and the algorithm and parameters of SantaLucia (Proc.Natl. Acad. Sci. 95:1460-65 (1998)). Descriptions of identifyingportions can be found in, among other places, U.S. Pat. No. 6,309,829(referred to as “tag segment” therein); U.S. Pat. No. 6,451,525(referred to as “tag segment” therein); U.S. Pat. No. 6,309,829(referred to as “tag segment” therein); U.S. Pat. No. 5,981,176(referred to as “grid oligonucleotides” therein); U.S. Pat. No.5,935,793 (referred to as “identifier tags” therein); and PCTPublication No. WO 01/92579 (referred to as “addressablesupport-specific sequences” therein).

In some embodiments, the stem and/or loop of the loopable primer cancomprise an identifying portion, and the detector probe can hybridize tothe corresponding identifying portion. In some embodiments, the detectorprobe can hybridize to both the identifying portion as well as sequencecorresponding to the target nucleic acid sequence. In some embodiments,at least two identifying portion: identifying portion complementduplexes have melting temperatures that fall within a ΔT_(m) range(T_(max)−T_(min)) of no more than 10° C. of each other. In someembodiments, at least two identifying portion-identifying portioncomplement duplexes have melting temperatures that fall within a ΔT_(m)range of 5° C. or less of each other. In some embodiments, at least twoidentifying portion-identifying portion complement duplexes have meltingtemperatures that fall within a ΔT_(m) range of 2° C. or less of eachother.

In some embodiments, at least one identifying portion or at least oneidentifying portion complement is used to separate the element to whichit is bound from at least one other component of a ligation reactioncomposition, a digestion reaction composition, an amplified ligationreaction composition, or the like. In some embodiments, identifyingportions are used to attach at least one ligation product, at least oneligation product surrogate, or combinations thereof, to at least onesubstrate. In some embodiments, at least one ligation product, at leastone ligation product surrogate, or combinations thereof, comprise thesame identifying portion. Examples of separation approaches include butare not limited to, separating a multiplicity of differentelement-identifying portion species using the same identifying portioncomplement, tethering a multiplicity of different element-identifyingportion species to a substrate comprising the same identifying portioncomplement, or both. In some embodiments, at least one identifyingportion complement comprises at least one label, at least one mobilitymodifier, at least one label binding portion, or combinations thereof.In some embodiments, at least one identifying portion complement isannealed to at least one corresponding identifying portion and,subsequently, at least part of that identifying portion complement isreleased and detected, see for example Published P.C.T. ApplicationWO04/4634 to Rosenblum et al., and Published P.C.T. ApplicationWO01/92579 to Wenz et al.

As will be appreciated by one of skill in the art, while the presentlydisclosed looped primers can include an identifying portion, it need notbe included and is not included in some embodiments. In someembodiments, the loopable primer includes an identifying portion as wellas the noncomplementary region. Is some embodiments, the identifyingportion is not the same as the noncomplementary region. In someembodiments, an identifying portion is not included in a loopableprimer.

As used herein, the term “extension reaction” refers to an elongationreaction in which the 3′ target specific portion of a loopable primer isextended to form an extension reaction product comprising a strandcomplementary to a target nucleic acid sequence. In some embodiments,the target nucleic acid sequence is a gDNA molecule or fragment thereof.In some embodiments, the target nucleic acid sequence is a short DNAmolecule and the extension reaction comprises a polymerase and resultsin the synthesis of a 2^(nd) strand of DNA. In some embodiments, theconsolidation of the extension reaction and a subsequent amplificationreaction is further contemplated by the present teachings.

As used herein, the term “primer portion” refers to a region of apolynucleotide sequence that can serve directly, or by virtue of itscomplement, as the template upon which a primer can anneal for any of avariety of primer nucleotide extension reactions known in the art (forexample, PCR). It will be appreciated by those of skill in the art thatwhen two primer portions are present on a single polynucleotide, theorientation of the two primer portions is generally different. Forexample, one PCR primer can directly hybridize to a first primerportion, while another PCR primer can hybridize to the complement of thesecond primer portion. In some embodiments, “universal” primers andprimer portions as used herein are generally chosen to be as unique aspossible given the particular assays and sequences involved to ensurespecificity of the assay. However, as will be appreciated by one ofskill in the art, when a noncomplementary region is employed, the needfor uniqueness with regard to the universal region is greatly diminishedif not removed completely.

The term “tail region” of a primer denotes a section at the 5′ end of aprimer sequence. In some embodiments this section can hybridize to partof a target sequence or priming site (e.g., such that the entire primeris hybridized to a target sequence or priming site). In someembodiments, the tail region has a sequence that is not complementary tothe nucleic acid sequence that the remaining portion of the primer hashybridized to (e.g., the 5′ end is not hybridized to a priming sitewhile the rest of the primer can hybridize). In some embodiments,primers having different tail regions are used so as to allow for asequence difference to be made at each end of the nucleic acid sequence(e.g., as shown in FIG. 7). Such a tail region can be denoted as a“noncomplementary tail region” or a second tail region, wherein thesecond tail region is different from the first. In some embodiments, thetail portion can include a zip-code, which can allow for theidentification or tracking of the molecule associated with the zip-code.In some embodiments, the tail portion of the forward primer is between5-8 nucleotides long. As will be appreciated by one of skill in the art,the length of the tail can determine the stability of the stem loop. Ifprimer dimers are not a significant problem, the tail can be, forexample, as large as a 20-mer to allow for the incorporation of forwardand reverse primers for sequencing reactions that require two differentprimers. In some embodiments, one can reduce potential primer-dimerformation from carry over random primers by using tails that are lessthan 5-8 nucleotides in length. In some embodiments, a noncomplementarytail region is not used.

In some embodiments, the tail portion of the forward primer is 6nucleotides long. Those in the art will appreciate that forward primertail portion lengths shorter than 5 nucleotides and longer than 8nucleotides can be identified in the course of routine methodology andwithout undue experimentation, and that such shorter and longer forwardprimer tail portion lengths are contemplated by the present teachings.

The term “upstream” as used herein takes on its customary meaning inmolecular biology, and refers to the location of a region of apolynucleotide that is on the 5′ side of a “downstream” region.Correspondingly, the term “downstream” refers to the location of aregion of a polynucleotide that is on the 3′ side of an “upstream”region.

As used herein, the term “hybridization” refers to the complementarybase-pairing interaction of one nucleic acid with another nucleic acidthat results in formation of a duplex, triplex, or other higher-orderedstructure, and is used herein interchangeably with “annealing.”Typically, the primary interaction is base specific, e.g., A/T and G/C,by Watson/Crick and Hoogsteen-type hydrogen bonding. Base-stacking andhydrophobic interactions can also contribute to duplex stability.Conditions for hybridizing detector probes and primers to complementaryand substantially complementary target sequences are well known, e.g.,as described in Nucleic Acid Hybridization, A Practical Approach, B.Hames and S. Higgins, eds., IRL Press, Washington, D.C. (1985) and J.Wetmur and N. Davidson, Mol. Biol. 31:349 et seq. (1968). In general,whether such annealing takes place is influenced by, among other things,the length of the polynucleotides and the complementarity, the pH, thetemperature, the presence of mono- and divalent cations, the proportionof G and C nucleotides in the hybridizing region, the viscosity of themedium, and the presence of denaturants. Such variables influence thetime required for hybridization. Thus, the preferred annealingconditions will depend upon the particular application. Such conditions,however, can be routinely determined by the person of ordinary skill inthe art without undue experimentation. It will be appreciated thatcomplementarity need not be perfect; there can be a small number of basepair mismatches that will minimally interfere with hybridization betweenthe target sequence and the single stranded nucleic acids of the presentteachings. However, if the number of base pair mismatches is so greatthat no hybridization can occur under minimally stringent conditionsthen the sequence is generally not a complementary target sequence.Thus, complementarity herein is meant that the probes or primers aresufficiently complementary to the target sequence to hybridize under theselected reaction conditions to achieve the ends of the presentteachings. Something is “configured to hybridize” when its sequence(e.g., structure) allows hybridization through base specific, e.g., A/Tand G/C, by Watson/Crick and Hoogsteen-type hydrogen bonding.

As used herein, the term “amplifying” refers to any method by which atleast a part of a target nucleic acid sequence, target nucleic acidsequence surrogate, or combinations thereof, is reproduced, typically ina template-dependent manner, including without limitation, a broad rangeof techniques for amplifying nucleic acid sequences, either linearly orexponentially. Exemplary means for performing an amplifying step includeligase chain reaction (LCR), ligase detection reaction (LDR), ligationfollowed by Q-replicase amplification, PCR, primer extension, stranddisplacement amplification (SDA), hyperbranched strand displacementamplification, multiple displacement amplification (MDA), nucleic acidstrand-based amplification (NASBA), two-step multiplexed amplifications,rolling circle amplification (RCA) and the like, including multiplexversions or combinations thereof, for example but not limited to,OLA/PCR, PCR/OLA, LDR/PCR, PCR/PCR/LDR, PCR/LDR, LCR/PCR, PCR/LCR (alsoknown as combined chain reaction-CCR), and the like. Descriptions ofsuch techniques can be found in, among other places, Sambrook et al.Molecular Cloning, 3.sup.rd Edition; Ausbel et al.; PCR Primer: ALaboratory Manual, Diffenbach, Ed., Cold Spring Harbor Press (1995); TheElectronic Protocol Book, Chang Bioscience (2002), Msuih et al., J.Clin. Micro. 34:501-07 (1996); The Nucleic Acid Protocols Handbook, R.Rapley, ed., Humana Press, Totowa, N.J. (2002); Abramson et al., CurrOpin Biotechnol. 1993 February; 4(1):41-7, U.S. Pat. No. 6,027,998; U.S.Pat. No. 6,605,451, Barany et al., PCT Publication No. WO 97/31256; Wenzet al., PCT Publication No. WO 01/92579; Day et al., Genomics, 29(1):152-162 (1995), Ehrlich et al., Science 252:1643-50 (1991); Innis etal., PCR Protocols: A Guide to Methods and Applications, Academic Press(1990); Favis et al., Nature Biotechnology 18:561-64 (2000); and Rabenauet al., Infection 28:97-102 (2000); Belgrader, Barany, and Lubin,Development of a Multiplex Ligation Detection Reaction DNA Typing Assay,Sixth International Symposium on Human Identification, 1995 (availableon the world wide web at:promega.com/geneticidproc/ussymp6proc/blegrad.html); LCR Kit InstructionManual, Cat. #200520, Rev. #050002, Stratagene, 2002; Barany, Proc.Natl. Acad. Sci. USA 88:188-93 (1991); Bi and Sambrook, Nucl. Acids Res.25:2924-2951 (1997); Zirvi et al., Nucl. Acid Res. 27:e40i-viii (1999);Dean et al., Proc Natl Acad Sci USA 99:5261-66 (2002); Barany andGelfand, Gene 109:1-11 (1991); Walker et al., Nucl. Acid Res. 20:1691-96(1992); Polstra et al., BMC Inf. Dis. 2:18-(2002); Lage et al., GenomeRes. 2003 February; 13(2):294-307, and Landegren et al., Science241:1077-80 (1988), Demidov, V., Expert Rev Mol. Diagn. 2002 November;2(6):542-8., Cook et al., J Microbiol Methods. 2003 May; 53(2):165-74,Schweitzer et al., Curr Opin Biotechnol. 2001 February; 12(1):21-7, U.S.Pat. No. 5,830,711, U.S. Pat. No. 6,027,889, U.S. Pat. No. 5,686,243,Published P.C.T. Application WO0056927A3, and Published P.C.T.Application WO9803673A1. In some embodiments, newly-formed nucleic acidduplexes are not initially denatured, but are used in theirdouble-stranded form in one or more subsequent steps. An extensionreaction is an amplifying technique that comprises elongating a loopableprimer that is annealed to a template in the 5′ to 3′ direction using anamplifying means such as a polymerase and/or reverse transcriptase.According to some embodiments, with appropriate buffers, salts, pH,temperature, and nucleotide triphosphates, including analogs thereof,i.e., under appropriate conditions, a polymerase incorporatesnucleotides complementary to the template strand starting at the 3′-endof an annealed loopable primer, to generate a complementary strand. Insome embodiments, the polymerase used for extension lacks orsubstantially lacks 5′ exonuclease activity. In some embodiments of thepresent teachings, unconventional nucleotide bases can be introducedinto the amplification reaction products and the products treated byenzymatic (e.g., glycosylases) and/or physical-chemical means in orderto render the product incapable of acting as a template for subsequentamplifications. In some embodiments, uracil can be included as anucleobase in the reaction mixture, thereby allowing for subsequentreactions to decontaminate carryover of previous uracil-containingproducts by the use of uracil-N-glycosylase (see for example PublishedP.C.T. Application WO9201814A2). In some embodiments of the presentteachings, any of a variety of techniques can be employed prior toamplification in order to facilitate amplification success, as describedfor example in Radstrom et al., Mol. Biotechnol. 2004 February;26(2):13346. In some embodiments, amplification can be achieved in aself-contained integrated approach comprising sample preparation anddetection, as described for example in U.S. Pat. Nos. 6,153,425 and6,649,378. Reversibly modified enzymes, for example but not limited tothose described in U.S. Pat. No. 5,773,258, are also within the scope ofthe disclosed teachings. The present teachings also contemplate variousuracil-based decontamination strategies, wherein for example uracil canbe incorporated into an amplification reaction, and subsequentcarry-over products removed with various glycosylase treatments (see forexample U.S. Pat. No. 5,536,649, and U.S. Provisional Application60/584,682 to Andersen et al.). Those in the art will understand thatany protein with the desired enzymatic activity can be used in thedisclosed methods and kits. Descriptions of DNA polymerases, includingreverse transcriptases, uracil N-glycosylase, and the like, can be foundin, among other places, Twyman, Advanced Molecular Biology, BIOSScientific Publishers, 1999; Enzyme Resource Guide, rev. 092298,Promega, 1998; Sambrook and Russell; Sambrook et al.; Lehninger; PCR:The Basics; and Ausbel et al.

As used herein, the term “detector probe” refers to a molecule used inan amplification reaction, typically for quantitative or real-time PCRanalysis, as well as end-point analysis. Such detector probes can beused to monitor the amplification of the target nucleic acid sequence.In some embodiments, detector probes present in an amplificationreaction are suitable for monitoring the amount of amplicon(s) producedas a function of time. Such detector probes include, but are not limitedto, the 5′-exonuclease assay (TAQMAN® probes described herein (see alsoU.S. Pat. No. 5,538,848) various stem-loop molecular beacons (see e.g.,U.S. Pat. Nos. 6,103,476 and 5,925,517 and Tyagi and Kramer, 1996,Nature Biotechnology 14:303-308), stemless or linear beacons (see, e.g.,WO 99/21881), PNA Molecular Beacons™ (see, e.g., U.S. Pat. Nos.6,355,421 and 6,593,091), linear PNA beacons (see, e.g., Kubista et al.,2001, SPIE 4264:53-58), non-FRET probes (see, e.g., U.S. Pat. No.6,150,097), Sunrise®/Amplifluor™ probes (U.S. Pat. No. 6,548,250),stem-loop and duplex Scorpion probes (Solinas et al., 2001, NucleicAcids Research 29:E96 and U.S. Pat. No. 6,589,743), bulge loop probes(U.S. Pat. No. 6,590,091), pseudo knot probes (U.S. Pat. No. 6,589,250),cyclicons (U.S. Pat. No. 6,383,752), MGB Eclipse™ probe (EpochBiosciences), hairpin probes (U.S. Pat. No. 6,596,490), peptide nucleicacid (PNA) light-up probes, self-assembled nanoparticle probes, andferrocene-modified probes described, for example, in U.S. Pat. No.6,485,901; Mhlanga et al., 2001, Methods 25:463-471; Whitcombe et al.,1999,. Nature Biotechnology. 17:804-807; Isacsson et al., 2000,Molecular Cell Probes. 14:321-328; Svanvik et al., 2000, Anal Biochem.281:26-35; Wolffs et al., 2001, Biotechniques 766:769-771; Tsourkas etal., 2002, Nucleic Acids Research. 30:4208-4215; Riccelli et al., 2002,Nucleic Acids Research 30:4088-4093; Zhang et al., 2002 Shanghai.34:329-332; Maxwell et al., 2002, J. Am. Chem. Soc. 124:9606-9612;Broude et al., 2002, Trends Biotechnol. 20:249-56; Huang et al., 2002,Chem. Res. Toxicol. 15:118-126; and Yu et al., 2001, J. Am. Chem. Soc14:11155-11161. Detector probes can also comprise quenchers, includingwithout limitation black hole quenchers (Biosearch), Iowa Black (IDT),QSY quencher (Molecular Probes), and Dabsyl and Dabcelsulfonate/carboxylate Quenchers (Epoch). Detector probes can alsocomprise two probes, wherein for example a fluor is on one probe, and aquencher is on the other probe, wherein hybridization of the two probestogether on a target quenches the signal, or wherein hybridization onthe target alters the signal signature via a change in fluorescence.Detector probes can also comprise sulfonate derivatives of fluorescenindyes with SO₃ instead of the carboxylate group, phosphoramidite forms offluorescein, phosphoramidite forms of CY 5 (commercially available forexample from Amersham). In some embodiments, interchelating labels areused such as ethidium bromide, SYBR® Green I (Molecular Probes), andPicoGreen® (Molecular Probes), thereby allowing visualization inreal-time, or end point, of an amplification product in the absence of adetector probe. In some embodiments, real-time visualization cancomprise both an intercalating detector probe and a sequence-baseddetector probe can be employed. In some embodiments, the detector probeis at least partially quenched when not hybridized to a complementarysequence in the amplification reaction, and is at least partiallyunquenched when hybridized to a complementary sequence in theamplification reaction. In some embodiments, the detector probes of thepresent teachings have a Tm of 63-69° C., though it will be appreciatedthat guided by the present teachings routine experimentation can resultin detector probes with other Tms. In some embodiments, probes canfurther comprise various modifications such as a minor groove binder(see for example U.S. Pat. No. 6,486,308) to further provide desirablethermodynamic characteristics. In some embodiments, detector probes cancorrespond to identifying portions or identifying portion complements.

The term “corresponding” as used herein refers to a specificrelationship between the elements to which the term refers. Somenon-limiting examples of corresponding include: a loopable primer cancorrespond with a target nucleic acid sequence, and vice versa. Aforward primer can correspond with a target nucleic acid sequence, andvice versa. In some cases, the corresponding elements can becomplementary. In some cases, the corresponding elements are notcomplementary to each other, but one element can be complementary to thecomplement of another element.

The term “or combinations thereof” as used herein refers to allpermutations and combinations of the listed items preceding the term.For example, “A, B, C, or combinations thereof” is intended to includeat least one of: A, B, C, AB, AC, BC, or ABC, and if order is importantin a particular context, also BA, CA, CB, CBA, BCA, ACB, BAC, or CAB.Continuing with this example, expressly included are combinations thatcontain repeats of one or more item or term, such as BB, AAA, MB, BBC,AAABCCCC, CBBAAA, CABABB, and so forth. The skilled artisan willunderstand that typically there is no limit on the number of items orterms in any combination, unless otherwise apparent from the context.

As used herein, the term “reaction vessel” or “reaction chamber”generally refers to any container in which a reaction can occur inaccordance with the present teachings. In some embodiments, a reactionvessel can be an eppendorf tube or other container of the sort in commonuse in modern molecular biology laboratories. In some embodiments, areaction vessel can be a well in microtitre plate, a spot on a glassslide, or a well in an Applied Biosystems TaqMan Low Density Array forgene expression (formerly MicroCard™). A plurality of reaction vesselscan reside on the same support. In some embodiments, lab-on-a-chip likedevices, available for example from Caliper and Fluidgm, can provide forreaction vessels. In some embodiments, various microfluidic approachesas described in U.S. Provisional Application 60/545,674 to Wenz et al.,can be employed. It will be recognized that a variety of reactionvessels are available in the art and within the scope of the presentteachings.

As used herein, the term “detection” refers to a way of determining thepresence and/or quantity and/or identity of a target nucleic acidsequence. In some embodiments, the sequence to be detected is known.Thus, in some embodiments, detection occurs by determining if the targetnucleic acid sequence comprises or consists of a known nucleic acidsequence, gene, etc. In some embodiments, the sequence to be detected isnot known prior to the experiment. In such embodiments, the targetnucleic acid sequence is amplified and sequenced. The sequencing of thetarget nucleic acid can be characterized as “detecting” the targetnucleic acid. The target nucleic acid sequence to be sequenced can beknown or unknown prior to its sequencing. Thus, in some embodiments, atarget nucleic acid is sequenced to determine if a specific sequence orgene is present in a sample, and/or determine what specific variant ispresent. In some embodiments, a target nucleic acid is sequenced todetermine the sequences of the genes or nucleic acid sequencesthemselves (e.g., the sequence and/or identity of the target nucleicacid sequence is not known prior to sequencing).

In some embodiments employing a donor moiety and signal moiety, one canuse certain energy-transfer fluorescent dyes for detection. Certainnonlimiting exemplary pairs of donors (donor moieties) and acceptors(signal moieties) are illustrated, e.g., in U.S. Pat. Nos. 5,863,727;5,800,996; and 5,945,526. Use of some combinations of a donor and anacceptor have been called FRET (Fluorescent Resonance Energy Transfer).In some embodiments, fluorophores that can be used as signaling probesinclude, but are not limited to, rhodamine, cyanine 3 (Cy 3), cyanine 5(Cy 5), fluorescein, VIC®, LIZ®, TAMRA™ (carboxytetramethylrhodamine,succinimidyl ester), 5-FAM™ (5-carboxyfluorescein), 6-FAM™(6-carboxyfluorescein), and Texas Red (Molecular Probes). (VIC®, LIZ®,TAMRA™, 5-FAM™, and 6-FAM™ all available from Applied Biosystems, FosterCity, Calif.).

In some embodiments, the amount of detector probe that gives afluorescent signal in response to an excited light typically relates tothe amount of nucleic acid produced in the amplification reaction. Thus,in some embodiments, the amount of fluorescent signal is related to theamount of product created in the amplification reaction. In suchembodiments, one can therefore measure the amount of amplificationproduct by measuring the intensity of the fluorescent signal from thefluorescent indicator. According to some embodiments, one can employ aninternal standard to quantify the amplification product indicated by thefluorescent signal. See, e.g., U.S. Pat. No. 5,736,333. Devices havebeen developed that can perform a thermal cycling reaction withcompositions containing a fluorescent indicator, emit a light beam of aspecified wavelength, read the intensity of the fluorescent dye, anddisplay the intensity of fluorescence after each cycle. Devicescomprising a thermal cycler, light beam emitter, and a fluorescentsignal detector, have been described, e.g., in U.S. Pat. Nos. 5,928,907;6,015,674; and 6,174,670, and include, but are not limited to the ABIPrism® 7700 Sequence Detection System (Applied Biosystems, Foster City,Calif.), the ABI GeneAmp® 5700 Sequence Detection System (AppliedBiosystems, Foster City, Calif.), the ABI GeneAmp® 7300 SequenceDetection System (Applied Biosystems, Foster City, Calif.), and the ABIGeneAmp® 7500 Sequence Detection System (Applied Biosystems). In someembodiments, each of these functions can be performed by separatedevices. For example, if one employs a Q-beta replicase reaction foramplification, the reaction does not need to take place in a thermalcycler, but could include a light beam emitted at a specific wavelength,detection of the fluorescent signal, and calculation and display of theamount of amplification product. In some embodiments, combined thermalcycling and fluorescence detecting devices can be used for precisequantification of target nucleic acid sequences in samples. In someembodiments, fluorescent signals can be detected and displayed duringand/or after one or more thermal cycles, thus permitting monitoring ofamplification products as the reactions occur in “real time.” In someembodiments, one can use the amount of amplification product and numberof amplification cycles to calculate how much of the target nucleic acidsequence was in the sample prior to amplification.

In some embodiments, one can simply monitor the amount of amplificationproduct after a predetermined number of cycles sufficient to indicatethe presence of the target nucleic acid sequence in the sample. Oneskilled in the art can easily determine, for any given sample type,primer sequence, and reaction condition, how many cycles are sufficientto determine the presence of a given target nucleic acid sequence. Asused herein, determining the presence of a target can compriseidentifying it, as well as optionally quantifying it. In someembodiments, the amplification products can be scored as positive ornegative as soon as a given number of cycles is complete. In someembodiments, the results can be transmitted electronically directly to adatabase and tabulated. Thus, in some embodiments, large numbers ofsamples can be processed and analyzed with less time and labor when suchan instrument is used.

In some embodiments, different detector probes can distinguish betweendifferent target nucleic acid sequences. A non-limiting example of sucha probe is a 5′-nuclease fluorescent probe, such as a TaqMan® probemolecule, wherein a fluorescent molecule is attached to afluorescence-quenching molecule through an oligonucleotide link element.In some embodiments, the oligonucleotide link element of the 5′-nucleasefluorescent probe binds to a specific sequence of an identifying portionor its complement. In some embodiments, different 5′-nucleasefluorescent probes, each fluorescing at different wavelengths, candistinguish between different amplification products within the sameamplification reaction. For example, in some embodiments, one could usetwo different 5′-nuclease fluorescent probes that fluoresce at twodifferent wavelengths (WL_(A) and WL_(B)) and that are specific to twodifferent stem regions of two different extension reaction products (A′and B′, respectively). Amplification product A′ is formed if targetnucleic acid sequence A is in the sample, and amplification product B′is formed if target nucleic acid sequence B is in the sample. In someembodiments, amplification product A′ and/or B′ can form even if theappropriate target nucleic acid sequence is not in the sample, but suchoccurs to a measurably lesser extent than when the appropriate targetnucleic acid sequence is in the sample. After amplification, one candetermine which specific target nucleic acid sequences are present inthe sample based on the wavelength of signal detected and theirintensity. Thus, if an appropriate detectable signal value of onlywavelength WL_(A) is detected, one would know that the sample includestarget nucleic acid sequence A, but not target nucleic acid sequence B.If an appropriate detectable signal value of both wavelengths WL_(A) andWL_(B) are detected, one would know that the sample includes both targetnucleic acid sequence A and target nucleic acid sequence B.

In some embodiments, detection can occur through any of a variety ofmobility dependent analytical techniques based on differential rates ofmigration between different analyte species. Exemplarymobility-dependent analysis techniques include electrophoresis,chromatography, mass spectroscopy, sedimentation, e.g., gradientcentrifugation, field-flow fractionation, multi-stage extractiontechniques, and the like. In some embodiments, mobility probes can behybridized to amplification products, and the identity of the targetnucleic acid sequence determined via a mobility dependent analysistechnique of the eluted mobility probes, as described for example inPublished P.C.T. Application WO04/46344 to Rosenblum et al., andWO01/92579 to Wenz et al. In some embodiments, detection can be achievedby various microarrays and related software such as the AppliedBiosystems Array System with the Applied Biosystems 1700Chemiluminescent Microarray Analyzer and other commercially availablearray systems available from Affymetrix, Agilent, Illumina, and AmershamBiosciences, among others (see also Gerry et al., J. Mol. Biol.292:251-62, 1999; De Bellis et al., Minerva Biotec 14:247-52, 2002; andStears et al., Nat. Med. 9:14045, including supplements, 2003). It willalso be appreciated that detection can comprise reporter groups that areincorporated into the reaction products, either as part of labeledprimers or due to the incorporation of labeled dNTPs during anamplification, or attached to reaction products, for example but notlimited to, via hybridization tag complements comprising reporter groupsor via linker arms that are integral or attached to reaction products.Detection of unlabeled reaction products, for example using massspectrometry, is also within the scope of the current teachings.

In some embodiments, the term “universal region” as used herein refersto a region of an oligonucleotide primer that is designed to have nosignificant homology to any segment in the genome. However, as will beappreciated by one of skill in the art, given that the universal regioncan be included within the looped section of the loopable primer, therisk of nonspecific priming is greatly reduced, thereby removing thisrequirement for embodiments in which the universal region is within aloopable primer. Similarly, given that, in some embodiments, anoncomplementary region is included in the loopable primer, nonspecificpriming can be further reduced. Thus, in some embodiments, the universalregion is a region that allows for priming with a known primer. In someembodiments, this primer is common to at least one other nucleic acidsequences. In some embodiments, the “universal region” meets all therequirements for a normal oligonucleotide primer, such as lack ofsecondary structure, an appropriate Tm, and an appropriate GC contentand can be between about 8 and 35 bases in length, between about 15 and25 bases in length or between about 18 and 22 bases in length. However,as will be appreciated by one of skill in the art, the universal region,when part of the loopable primer, will be part of a larger structurethat has secondary structure. Additionally, because the universal regionwill be part of a larger primer, the universal region need only functionas part of the entire loopable primer. As such, in these embodiments,the universal region need only assist in priming, as described in detailbelow. In other embodiments, the universal region functionsindependently as a priming site. In some embodiments, the universalregion is the same as the noncomplementary region or they share some ofthe same nucleic acid sequences. “Universal priming site” when usedherein refers to a “universal region” of a primer that can function as asite to which universal primers anneal for priming of further cycles ofDNA amplification. In some embodiments, the loopable primer includes auniversal region. The term “universal primer” as used herein refers to aprimer that includes only a “universal region”.

The term “anneal” as used herein refer to the base-pairing interactionof one polynucleotide with another polynucleotide that results in theformation of a duplex or other higher-ordered structure. The primaryinteraction is base specific, i.e., A/T and G/C, by Watson/Crick andHoogsteen-type hydrogen bonding.

The term “real-time analysis” refers to periodic monitoring during PCR.Certain systems such as the ABI 7700 and 7900HT Sequence DetectionSystems (Applied Biosystems, Foster City, Calif.) conduct monitoringduring each thermal cycle at a predetermined or user-defined point.Real-time analysis of PCR with FRET probes measures fluorescent dyesignal changes from cycle-to-cycle, preferably minus any internalcontrol signals.

The term “5′-nuclease analysis” or “5′-nuclease assay” when used hereinrefers to “real-time analysis” for quantification of the amount of DNAamplified in a particular PCR reaction. TAQMAN® analysis is an exampleof such “5′-nuclease analysis” (a commercially available PCR kit).“5′-nuclease analysis” involves the use of a fluorogenic oligonucleotideprobe to which a reporter dye and a quencher dye are attached. Duringamplification of a nucleotide sequence using a forward and reverseprimer, the probe anneals to the target of interest between the forwardand reverse primer sites. During extension, the probe is cleaved by the5′-nuclease activity of the DNA polymerase. As the cleavage separatesthe reporter dye from the quencher dye, the reporter dye's fluorescenceincreases which can be detected and quantitated. Real-time analysis ofPCR with 5′-nuclease assay involves FRET probes that can be displayed byplotting the logarithmic change in detected fluorescence (ΔRn) versusthe cycle number. The cycle within the PCR protocol at which the changein fluorescence (ΔRn) rises above a threshold value is denoted as C_(T).The C_(T) cycle is approximately the cycle at which amplification oftarget becomes exponential. A relatively low C_(T) value indicatesefficient detection of amplicon. The threshold cycle is highlycorrelated to the amount of copy number, or amount of target nucleicacid sequence present in the sample, as well as the efficiency ofamplification. The effects of primer constitution, e.g. length,sequence, mismatches, analogs, can be conveniently screened andquantitated by measurement of C_(T) values during real-time analysis ofPCR. In some embodiments, the sequences within the insert sections canbe detected and/or amplified via a TAQMAN® assay or similar assay.

“Polymerase chain reaction” or “PCR” as used herein, refers to a methodin the art for amplification of a nucleic acid. The method can involveintroducing a molar excess of two or more extendable oligonucleotideprimers to a reaction mixture comprising the desired target sequence(s),where the primers hybridize to opposite strands of the double strandedtarget sequence. The reaction mixture is subjected to a program ofthermal cycling in the presence of a DNA polymerase, resulting in theamplification of the desired target sequence flanked by theoligonucleotide primers. The oligonucleotide primers prime multiplesequential rounds of DNA synthesis, each round of synthesis is typicallyseparated by a melting and re-annealing step. Methods for a wide varietyof PCR applications are widely known in the art, and are described inmany sources, for example, Ausubel et al. (eds.), Current Protocols inMolecular Biology, Section 15, John Wiley & Sons, Inc., New York (1994).

“In silico PCR” when used herein refers to a computer-conducted methodfor predicting the size and probability of amplification of a nucleotidesequence using a particular set of primers. The method involvessearching a DNA database for exact matches to the primer sequences andfurther for sequences having the correct order, orientation, and spacingto allow priming of amplification of a nucleotide sequence of apredicted size.

“Tm” as used herein, refers to the melting temperature (temperature atwhich 50% of the oligonucleotide is a duplex) of the oligonucleotidecalculated using the nearest-neighbor thermodynamic values of Breslaueret al. (Proc. Natl. Acad. Sci. USA 83:3746 3750, 1986) for DNA andFreier et al. (Proc. Natl. Acad. Sci. USA 83:9373 9377, 1986) for RNA.

As will be appreciated by one of skill in the art, the above definitionsoccasionally describe various embodiments that can also be used, in someembodiments, with the variously defined parts or steps. Unlessindicated, these various embodiments are not required or part of theactual definitions and have been included for additional general contextand for further description of the various contemplated embodiments.

Aspects of the present teachings can be further understood in light ofthe following description and examples, which should not be construed aslimiting the scope of the present teachings in any way.

Loopable Primers and Uses Thereof

There are numerous strategies for nucleic acid amplification involvingthe use of random or degenerate primers. These primers can be especiallyuseful in the amplification of unknown sequences, such as in wholegenome amplification. To date, many of the techniques have drawbacks,including issues such as primer-dimer formation or the accumulation ofother relatively short fragment artifacts that dominate PCR or otheramplification products.

In some embodiments, some or all of the above issue(s) can be addressedby using loopable primers to prime the target nucleic acid. In someembodiments, these loopable primers include a random or degeneratepriming sequence (or more generally 3′ target specific regions), auniversal region within the looped section, and, optionally, anoncomplementary region and have a reduced likelihood of formingprimer-dimers and/or resulting in other nonspecific priming events.

FIG. 1A depicts one embodiment of a loopable primer 6. The loopableprimer can include a 3′ target specific region 50, a first loop-formingregion 10, an optional noncomplementary region 30, a second loopforming-region 10′, and a universal region (also called a universalpriming region) 20.

As described in more detail below, the noncomplementary region 30 canhave various advantages in various embodiments. For example, byselecting a noncomplementary region that is relatively rare in themiddle of gDNA (such as a poly T sequence), one can reduce thelikelihood that spurious internal priming will occur in variousamplification steps. Additionally, when various universal regions areemployed, the presence of the noncomplementary region (which can be thesame across all of the loopable primers) can reduce the likelihood thatprimer-dimers will form.

As described in detail below, and outlined in FIG. 1B, in someembodiments, the loopable primer can be used to initiate priming asdesired (e.g., via a random or degenerate priming region), while stillincluding a universal and a noncomplementary region in the primer.Moreover, this can be achieved with a reduced risk of nonspecific orprimer-dimer interactions occurring.

In some embodiments, such as the one depicted in FIG. 1B, the use of theloopable primer to amplify sections of a target sequence allows one toplace complementary sequences on either end of the amplified targetnucleic acid sequence. As noted below, the addition of thesecomplementary sequences allow for the size dependent amplification ofthe target nucleic acid sequences.

The first step depicted in FIG. 1B is the addition of a loopable primer(6 depicted in FIG. 1A) to a solution that includes the target nucleicacid sequence or sequences that are to be amplified 110 or in which atarget is to be identified, if present. Conditions are selected suchthat the loopable primer hybridizes to the target sequence 120. Theloopable primer is then extended along the target sequence to form anextended loopable primer 130. One can then allow the loopable primer(the same degenerate loopable primer, an identical loopable primer, or adifferent loopable primer, as long as the same universal region ispresent) to hybridize to the extended loopable primer 140. Then one canextend the additional loopable primer along the extended loopable primerto form a double-extended loopable primer 150. In various embodiments,the loopable primers can have identical sequences; can have identicalsequences apart from the 3′ target specific region; can have differentsequences, apart from the noncomplementary region; or can have differentsequences, as long as the noncomplementary regions will effectivelyreduce nonspecific priming of the loopable primer.

In some embodiments, some or all of steps 110-150 can be repeated asdesired. In some embodiments, some or all of steps 110-150 can berepeated as desired prior to proceeding to step 160. Following the step150, one can optionally amplify the double-extended loopable primerusing an amplification primer 160. The amplification primer will have asequence that will hybridize to a sequence that is complementary to theuniversal region on the primer (e.g., the amplification primer can havea sequence that is or is a part of the universal region) and optionally(if necessary) a sequence that will hybridize to the noncomplementaryregion. As will be appreciated by one of skill in the art, in someembodiments, only one of these regions will be present.

One can then allow the shorter double-extended loopable primer toself-hybridize 170. In some embodiments, one can allow both the shortand the long double-extended loopable primers to self-hybridize. Thisself-hybridized population can then be used in the selectiveamplification of large insert sections over relatively small insertsections 180 (depicted in FIGS. 4 and 5). Thus, in some embodiments, theuse of the loopable primer described above results in a self-hybridizedpopulation that allows for the selective amplification of largersections of target nucleic acid sequences over smaller sections oftarget nucleic acid sequences contained within the self-hybridizedstructures. In some embodiments an initial reverse transcription stepcan be performed or a cleaning step can be included, for example asdescribed in the following sections.

While the self-hybridized structure can be used to help select largerinsert section (or insert sections) over smaller insert sections, thelarger double extended loopable primer need not assume a loopedconfiguration. For example, in some embodiments, the self-hybridizedstructure is only formed for the shorter insert sections. Thus, in someembodiments, selective amplification of longer insert sections overshorter insert sections (including primer dimers) occurs without theformation of a self-hybridized structure for the longer double extendedloopable primer. Without intending to be limited by theory, it isunderstood that because a shorter insert sections will mean that thereis less distance between the universal region and the universal regioncomplement, that these short double extended loopable primers will selfhybridize faster than double extended loopable primers with largerinsert sections. Similarly, the larger double-extended loopable primerswill have more distance between the loopable primer and its complementand thus it can take longer for the primer and its complement toself-hybridize. Thus, in some embodiments, it is the faster ability ofthe double extended loopable primers having shorter insert sections toself-hybridize, and thus take themselves out of a reaction, that allowsfor the selective amplification of the double extended loopable primershaving the longer insert sections over the shorter (or no foreign)insert sections. Thus, in some embodiments, the longer or long insertsection is not in a looped configuration during the selectiveamplification.

Additional embodiments of the method of using the loopable primers forthe selective amplification of relatively larger target nucleic acidsequences (compared to shorter target nucleic acid sequences) are showngenerally in FIG. 1C. The first step 200 can involve primer extensionvia the loopable primers described above (to form a double-extendedloopable primer) which can be followed by step 210, a digestion ofvarious random primers, such as with exonuclease I. In some embodiments,this is followed by a pre-PCR amplification step with a singleamplification primer (step 220). Following this, a step is performed toamplify the insert section, depending upon the size of the targetnucleic acid sequence within the insert section. This can be achievedwith an insert amplification primer (step 230). As shown in FIG. 1C bythe arrows, various steps can be included or removed for variousembodiments. In some embodiments, the cleaning step 225 is not performedor is performed after the pre-PCR amplification 220. In someembodiments, multiple rounds of cleaning (e.g., exonuclease digestion)are employed. Specific embodiments involved in these methods arediscussed in more detail in regard to FIGS. 2-7.

In the top section of FIG. 2, the loopable primer 6 is shown hybridizedat a first part 11 at a complementary portion of the target nucleic acidsequence 1 in a first arrangement 121. This results from a first step inwhich, the loopable primer 6 is allowed to anneal via the 3′ targetspecific region 50 to the first part of the target nucleic acid sequenceat a target binding site 11. Following the hybridization, the primer isextended along the target sequence in the 5′ direction of the targetsequence or in the 3′ direction from the loopable primer (arrow).Following this extension, an additional loopable primer 5 (which canhave the same sequence as the first loopable primer, a differentsequence (but same universal region 20, and/or the same 3′ targetspecific region 50 and/or noncomplementary region 30) hybridizes at acomplementary portion of the extended loopable primer 2 at a secondtarget binding site 12, as shown in FIG. 2, in a second arrangement 131.As above, the loopable primer 6 can include a 3′ specific target region50, a first loop-forming region 10, optionally a noncomplementary region30, a universal region 20, and a second loop-forming region 10′. In someembodiments, the loopable primers 5 and 6 are the same. In someembodiments, the loopable primers are the same, apart from their 3′target specific region 50.

In some embodiments, the 3′ target specific region is a degenerateregion; thus, identifier “50” can represent multiple or differentsequences on different primers as it can be a degenerate sequence. ForFIGS. 3-7, the 3′ target specific region is depicted as identifier 50and 52, (to provide additional clarity for some embodiments in which the3′ target specific region is degenerate), and thus the specificsequences of 50 and 52 are identified by different identifiers in thesefigures. However, both 50 and 52 are 3′ target specific regions (andthus can be the same in some embodiments). In addition, the 3′ targetspecific region identifier “50” can be used generically throughout asingle FIGURE (such as in FIG. 2), to denote different sequences, eventhough a single identifier is used (thus, both “50” and “52” need not bepresent to denote that a region is degenerate). One of skill in the artwill readily appreciate how this and other sequences within theseloopable primers 5 & 6 can be differed, if desired.

Following the hybridization of the loopable primer 6 to the extendedloopable primer 2 the loopable primer 6 is extended from its 3′direction to the 5′ direction of the extended loopable primer. Thisextension results in a double-extended loopable primer 4 (FIG. 3). Asnoted above, the term “double-extended loopable primer” does not implythat the sequence functions as a primer but that it is formed fromextending loopable primers.

The double-extended loopable primer can optionally be amplified at thispoint. This is shown in more detail in FIG. 3 in which an amplificationprimers 60 is used to amplify the double-extended loopable primer 4. Insome embodiments, the first amplification primer includes, comprises,consists, or consists essentially of a universal region. In someembodiments, the first amplification primer includes a sequence that isthe same as the noncomplementary region 30 of the first loopable primer,a sequence that is the same as the original universal region 20, andoptionally a sequence that is the same as the second loop-forming region10′. This amplification primer 60 can hybridize to the complement of thedouble-extended loopable primer allowing for efficient amplification ofthe double-extended loopable primer. In some embodiments, more than oneamplification primer can be used. In some embodiments, only a singleprimer per loopable primer nucleic acid sequence is used in theamplification step depicted in FIG. 3. In some embodiments, the use of asingle primer sequence that will not hybridize to the initial loopableprimer can help reduce nonspecific primer dimerization that couldotherwise occur due to the presence of an amplification primer andremaining loopable primers. Thus, by selecting an amplification primerthat has the same sequence as a portion of the loopable primer, one canfurther reduce the risk of primer dimerization or other nondesiredhybridization events. Of course, the presence of the noncomplementaryregion 30 in the loopable primer 6 can be exploited in selecting such anamplification primer 60. In some embodiments, the amplification of thedouble extended loopable primer results in the selective amplificationof double extended loopable primers having long insert sections overthose with shorter or no foreign insert sections.

As will be appreciated by one of skill in the art, the amplificationstep can occur in situations in which additional background DNA ornucleic acid sequences are present. As will be appreciated by one ofskill in the art, in embodiments in which the insert amplificationprimer only hybridizes to the universal region, there could besignificant priming events to non target sections. However, the presenceof the noncomplementary region in the loopable primer (and morespecifically sequences complementary to these regions in thedouble-extended loopable primer) and in the amplification primer reducethe likelihood that this will occur.

Following the optional amplification step, at least a subpopulation ofthe double-extended loopable primer can self-hybridize (as shown in FIG.5). As noted above, self-hybridization of the double extended loopableprimer does not have to occur for all species in a sample. Rather,self-hybridization need only occur for the shorter sequences (FIG. 5)which are to be reduced or “amplified over.” Thus, in some embodiments,self-hybridization occurs for the structures in FIG. 5, but not for thestructures depicted in FIG. 4. However, in some embodiments, the longerdouble-extended loopable primers also self-hybridize, as shown in FIG.4.

As will be appreciated by one of skill in the art, the portions of thedouble extended loopable primer corresponding to the universal region 20and the universal region complement 20′ are capable of hybridizing toone another. The insert section 9 itself can then have the targetnucleic acid sequence, or fragment thereof, which can be amplified byany of various reactions such as PCR. In some embodiments, insertamplification primer(s) 80 and/or 81 are used to amplify at least aportion of the insert. As will be appreciated by one of skill in theart, the size of the insert should be sufficient to allow amplification.

In embodiments in which self-hybridization of the longer double extendedloopable primers is not required to occur (e.g., does not occurfrequently or is not driving a subsequent selective amplification oflonger insert sections over shorter insert sections), then the selectiveamplification is believed to occur due to the fact that the shorterdouble-extended loopable primers self-hybridize more rapidly than thelonger double-extended loopable primers and thus are removed fromsubsequent rounds of amplification more quickly than the longerdouble-extended loopable primers. In such embodiments, whileself-hybridization still occurs for the shorter double-extended loopableprimers (e.g., primer dimers) it does not need to occur for the longerdouble-extended loopable primers. As the universal region and theuniversal region complement on these longer double-extended loopableprimers (as depicted in FIG. 4) are separated by more nucleotides thanthe shorter double-extended loopable primer (FIG. 5), theself-hybridization of the longer double-extended loopable primers willtake longer, allowing more time for the insert amplification primer tohybridize and extend. Thus, the self-hybridized structure for the longerdouble-extended loopable primer need not be formed to selectivelyamplify the longer double-extended loopable primer over the shorterdouble-extended loopable primer.

As will be appreciated by one of skill in the art, in embodiments inwhich whole genome amplification is being performed, the precisesequence within the insert section can be unknown. In light of this, itcan be advantageous to use multiple insert amplification primers to makecertain that one will prime and extend as desired. In some embodiments,a pool of insert amplification primers is used. In other embodiments,one insert amplification primer (and/or one set or more) is mixed withthe solution containing the double-extended loopable primer. As will beappreciated by one of skill in the art, numerous such mixtures (e.g.,2-10, 10-100, 100-1,000, 1,000-10,000 or more) can be done in series orin parallel. Furthermore, the solution containing the double-extendedloopable primer can be divided into parts so that the various reactionscan be run in parallel.

As will be appreciated by one of skill in the art, not every loopableprimer will necessarily hybridize to the target sequence as desired andin some embodiments a loopable primer duplex or primer dimer will beformed. Additionally, in some embodiments, loopable primers canhybridize to one another, also forming short amplification products.Additionally, in some embodiments, nonspecific hybridization or overlyfrequent hybridization of the 3′ target specific region or of othersections (such as the universal region) of the various primers canhybridize to sections of the target nucleic acid sequence can occur suchthat only these smaller sections of the target nucleic acid sequence.One depiction of the above is shown in FIG. 5. In such a situation,rather than having target nucleic acid sequence (or a significant amountof it) between the universal region 20 and the complement to theuniversal region 20′, there is an insignificant amount of targetsequence between the two 20 and 20′. As shown in FIG. 5, when theuniversal region 20 and universal region complement 20′ hybridizetogether under this situation, the insert section 109 in the complex 108is relatively small. In some embodiments, there is a nucleic acidsequence 51 in the insert section between the 3′ target specific region50 and its complement 52. This nucleic acid sequence 51 need not bepresent and, if it is present, is relatively short. In some embodiments(when a sufficiently large insert is present), the insert section 109(including sequence 51) is not more than 10 kb in length. In someembodiments, the insert section 109, while still capable of allowingamplification does so with relatively less efficiency than thedouble-extended loopable primer complex 8 shown in FIG. 4. As such,relative amplification of the product 8 shown in FIG. 4 can be achievedcompared to amplification of the resulting product 108 shown in FIG. 5.As will be appreciated by one of skill in the art, this distinctionbetween the two resulting products can reduce the role or impact thatnonspecific primer interactions can have, e.g., primer dimers on theability to identify amplified sequence target. That is, this distinctioncan generally improve target detection by reducing the impact of nucleicacid structures (or products) in which a significant or substantialamount of target DNA has not incorporated between the two primers. Aswill be appreciated by one of skill in the art, when the 3′ targetspecific region 50 and 52 are complementary to one another (e.g., whenonly a single palindromic sequence is used) they can hybridized togetherand the sequence 51 need not be present (e.g., when the double-extendedloopable primer is just a primer dimer). In embodiments in which the 3′target specific region is a degenerate region or sequence, then sections50 and 52 need not, and often will not, be complementary to one another.

While not depicted in FIGS. 4 and 5, one of skill in the art willreadily recognize that in the embodiments in which a self-hybridizedstructure is not created for the longer double-extended loopable primer,that the insert amplification primers 81 and 80 can bind to the “open”double-extended loopable primer, and can bind to the universal region orother section of the loopable primer. In some embodiments, one of theinsert amplification primers comprises, consists, or consistsessentially of a universal region, while the second insert amplificationprimer primes in the insert. In some embodiments, both insertamplification primers hybridize within the insert section. In someembodiments, neither of the insert amplification primers prime oroverlap with any section of the loopable primer.

Double-Extended Loopable Primers with Additional Specific Sequences

As will be appreciated by one of skill in the art, in some embodiments,it is desirable to have specific sequences on the 5′ and/or 3′ end ofthe nucleic acid sequence that have been amplified, such as thedouble-extended loopable primer. Examples of such specific sequencesinclude zip-code sequences, as described in U.S. Pat. Pub. No:2006/0014191 (the entirety of which is hereby incorporated byreference). One option for achieving this is shown in FIG. 6 and FIG. 7(which depict the self-hybridized embodiments only, although one ofskill in the art can adjust the figures for the non-self-hybridizedembodiments as well). In such embodiments, rather than (or following)the amplification step depicted in FIG. 3, involving the amplificationprimer 60, one performs an amplification step to add a desired sequence(e.g., 71) to one end of the double-extended loopable primer via adifferent primer 70. This process, and the resulting product 702, areshown in FIG. 6 for a double-extended loopable primer that has asignificant amount of target nucleic acid sequence in it, and in FIG. 7,for a double-extended loopable primer that has an insignificant amountof target DNA in it.

In some embodiments, there is a first amplification primer 70 which,while including the universal region 20 (and optionally thenoncomplementary region 30), includes an additional section 71. Thissection 71 allows one to customize the end(s) of the double-extendedloopable primer. As will be appreciated by one of skill in the art,section 71 is not a “noncomplementary” region, as defined herein,rather, it is a sequence that is not complementary to the sequence thatthe amplification primer 70 is hybridized to. The ability to havedifferent sequences on each end of the nucleic acid segment (which canbe achieved by using two different primers with different sections 71)can be useful in some sequencing applications. Thus, the aboveamplification primer 70 can be used in these situations. The primer 70can include the noncomplementary region 30 and the universal region 20.As will be appreciated by one of skill in the art, different primers 70,each having a different section 71, can be added to specific doubleextended loopable primers, allowing various double extended loopableprimers to be combined and processed in parallel, while still being ableto identify the specific double extended loopable primer. In someembodiments, two different primers or different sections can be added toeach end.

As shown in the lower section of FIG. 6, when the target nucleic acidsequence 1 is included, amplification proceeds from these two primers toproduce a double extended loopable primer (702). Of course, an actuallooped structure need not be formed and desirable reaction kinetics canbe sufficient to achieve the desired reactions.

In contrast, as shown in FIG. 7, in those situations in which verylittle or no target nucleic acid sequence is included between theuniversal region 20 and its complement 20′ (or the first loop formingregion 10 and the second loop forming region 10′), the resultingstructure has a relatively smaller insert section resulting inrelatively less amplification through the use of insert amplificationprimers (802) (as noted above, this can be due to the fasterhybridization kinetics due to the shorter linker and/or due to, forexample, the smaller size of the insert structure which can physicallylimit processing of this area.)

Additional Alternative Aspects

In some situations, after incorporation of a universal region, universalprimers can still have a problem of having some homology with internalsequences in highly complex populations of long gDNA fragments from thewhole genome. Where the concentration of the universal primers aretypically on a μM scale, even partial matches of the 3′ end of theuniversal primers with internal sequences of gDNA fragments can generateshorter products. These shorter products can be preferentially amplifiedby high concentrations of universal primers. Thus, some of the presentembodiments can be used to limit the generation of these short productsfrom primer-dimers or spurious internal priming. In some embodimentslong tracts of dT bases can be used in the loopable primer (as anoncomplementary region for example) for the above reason and becausethe frequency of poly dT in the middle of gDNAs can be low. In otherembodiments, tracts of sequences rarely found in the target genome areused as a noncomplementary region.

As will be appreciate by one of skill in the art, while the 3′ targetspecific region often includes a random or degenerate region, in someembodiments, the sequence is a specific sequence or collection ofspecific sequences. In some embodiments, the looped section of theloopable primer (including the stem) can include additional sequencesections to those described above. In other embodiments, the loopedsection only includes those depicted in FIG. 1A. Additionally, as willbe appreciated by one of skill in the art, some of the presentlydisclosed techniques can be applied to RNA amplification as well, forexample, by including an initial reverse transcription step.

As will be appreciated by one of skill in the art, in some embodiments,a noncomplementary region is used throughout numerous primers, allowingfor multiple primers, such as primers including universal, random, ordegenerate regions, to be used with a reduced risk of undesired primingevents. This can be useful in multiplexed reactions in which numerousdifferent starting primers are employed.

In some embodiments, the above methods can allow for a significantamount of amplification to occur. In some embodiments, the amplificationis of nucleic acid sequences of a significant length (e.g., 200 or morenucleic acids). In some embodiments, the amplification of these lengthsof target nucleic acid sequences, across a genome's worth of nucleicacid sequence, is achieved. In some embodiments, at least a fraction ofthe genome is amplified, e.g., 0-1, 1-5, 5-10, 10-20, 20-30, 30-40,40-50, 50-60, 60-70, 70-80, 80-90, 90-95, 95-99, or 99-100% of thegenome is amplified. In some embodiments, at least some fraction of thefraction amplified is of the desired length, e.g., 0-1, 1-5, 5-10,10-20, 20-30, 30-40, 40-50, 50-60, 60-70, 70-80, 80-90, 90-95, 95-99, or99-100% is at least 200 bp in length.

In some embodiments, the amount of amplification across a genome issubstantially similar. In some embodiments, the amount of amplificationfor the various target nucleic acids sequences is the same. In otherwords, sequences A-Z are all amplified to a similar extent so that theresulting ratio of product nucleic acid sequences is the substantiallythe same for sequences A-Z. In some embodiments, the ratios aremaintained in a qualitative manner (e.g., there is more of sequence Athan sequence B).

In some embodiments, the amount of amplification of the desiredfragments that is achieved is substantial. For example, amplification ofthe initial product over 30 fold can be achieved, e.g., 30-100,100-1000, 1,000-3000, 3000-10,000, 10,000-50,000, 50,000-100,000,100,000-500,000, 500,000-800,000, 800,000-1,000,000,1,000,000-10,000,000 fold or more. In some embodiments this is achievedwith a reduced amount of primer dimer formation and/or spurious priming.In some embodiments, the amount of primer dimers is reduced by at leastsome amount, e.g., 0-1, 1-5, 5-10, 10-20, 20-30, 30-40, 40-50, 50-60,60-70, 70-80, 80-90, 90-95, 95-99, or 99-100%.

As noted above, some of the embodiments can be advantageously used whenrandom and/or degenerate priming regions are employed at the 3′ targetspecific region of the primer, when universal primers are used, or whenboth aspects are used. Moreover, in some embodiments, further benefitscan be obtained when numerous such primers (or other non-loopableprimers) are combined within a reaction (such as in multiplexed orsubsequent amplification or extension reactions). As such, as notedabove, some of the embodiments can be useful for whole genomeamplification. However, not all of the disclosed embodiments are limitedto such applications. Even amplification reactions that do not includerandom regions, or do not involve whole genome amplification can benefitfrom some of the above embodiments. For example, some of the aboveembodiments will reduce the number or amount of relatively short nucleicacid sequences that are amplified from a target. As will be appreciatedby one of skill in the art, these shorter sequences can be problematicfor a variety of reasons (e.g., since they are shorter, they willdominate subsequent amplification reactions). Additionally, theinsertion of the noncomplementary region generally allows for one to useeither a random, specific, or mix thereof, region for targethybridization, while reducing the likelihood that the target sequencewill hybridize too frequently or nonspecifically.

In some embodiments, the loopable primers and relevant methods areemployed in massively multiplexed procedures in which various loopableprimers are employed. As will be appreciated by one of skill in the art,the above embodiments employing degenerate ends at the 3′ targetspecific region of the probe is one form of multiplexing. However, insome embodiments, different sequences are also employed within theloopable section and/or the stem section so as to provide a degree ofseparation or distinctness among the amplified products. In someembodiments, these different sequences are in the universal primingsection, a tag sequence, or other additional section added to theloopable primer. In some embodiments, the number of primers having thesedifferent sequences (apart from differences in the 3′ target specificregion) are at least 2, if not more, for example, 2-5, 5-10, 10-20,20-30, 30-50, 50-100, 100-200, or more primers can be used. In someembodiments, the primers can include specific bar-code sequences toallow for ease of identification. In some embodiments, these sequencesare the same as the stem forming sequences (e.g., the first and secondloop forming regions).

In some embodiments, the loopable primer and various embodimentsdisclosed herein are used for assisting in forensic analysis. In someembodiments, the loopable primer and various embodiments disclosedherein are employed in amplifying a target nucleic acid sequence for DNAfingerprinting. In some embodiments, the loopable primer and variousembodiments disclosed herein are employed in amplifying short tandemrepeats (“STR”) from a sample that is to be identified or matched toanother sample. In some embodiments, the loopable primer includes asequence that can be used to amplify a STR locus. In some embodiments,the insert amplification primer includes a sequence that can be used toamplify a STR locus.

In some embodiments, the double-extended loopable primer is created asdescribed by any of the embodiments described herein. Once the doubleextended loopable primer is created, and optionally amplified by anamplification primer, one or more insert amplification primers can beused to amplify the insert section. In some embodiments, the insertamplification primers will hybridize to sections upstream or downstreamof one or more STR loci to be amplified. In some embodiments, the insertamplification primer comprises or consists of a STR primer. Thus, insome embodiments, the double-extended loopable primer can be used forefficient amplification of a target or target genome and the use ofSTR-primers (or insert amplification primers that can be used to amplifya STR locus) can be used to further selectively amplify and/or detectthe presence of specific STRs in a sample. In some embodiments, theinsert amplification primer is a STR-primer that can amplify the locusof one or more of the 13 standard STRs examined for DNA fingerprinting.In some embodiments, the insert amplification primer is a STR-primerthat can amplify the locus of one or more of the currently 13 standardSTRs examined for DNA fingerprinting.

In some embodiments, rather than using a STR specific aspect towards theend of the process, the loopable primer itself comprises an aspect thatwill direct it to the amplification of STRs or sequences around STRs.For example, in some embodiments, the 3′ target specific region, ratherthan being a random or degenerate region, comprises or consists of aSTR-primer sequence that can be used to amplify a STR locus. Apart fromthis modification, the remaining steps can include any of thosedisclosed herein. In such an embodiment, the insert amplificationprimers do not need to be STR primers (although they can be).

A “STR-3′ target specific region” denotes a 3′ target specific regionthat will serve as a STR-primer (and thus can be used to amplify a STRlocus).

A “STR-primer” is a primer that can be used to amplify a STR locus.

In some embodiments, the locus is one or more of TH01, TPOX, CSF1PO,vWA, FGA, D3S1358, D5S818, D7S820, D13S317, D16S539, D8S1179, D18S51,D21S11, D2S1338, D3S1539, D4S2368, D9S930, D10S1239, D14S118, D14S548,D14S562, D16S490, D16S753, D17S1298, D17S1299, D19S253, D19S433,D20S481, D22S683, HUMCSF1PO, HUMTPOX, HUMTH01, HUMF13AO1, HUMBFXIII,HUMLIPOL, HUMvWFA31, Amelogenin, D12s391, D6S1043, SE33, or anycombination thereof. In some embodiments, the locus is one or more ofCSF1PO, FGA, TH01, TPOX, vWA, D3S1358, D5S818, D7S820, D8S1179, D13S317,D16S539, D18S51, D21S11, D19S433, and D2S1338. In some embodiments, thelocus is a “CODIS loci” or “CODIS locus.” This refers to the STR locidesignated by the FBI's “Combined DNA Index System.” Thirteen core STRloci are TH01, TPOX, CSF1PO, vWA, FGA, D3S1358, D5S818, D7S820, D13S317,D16S539, D8S1179, D18S51, and D21S11. (See, e.g., Butler, Forensic DNATyping, Academic Press (2001), at page 63.)

In some embodiments, more than one locus is amplified in one reaction.In some embodiments, two, three, four, five, six, seven, eight, nine,ten, eleven, twelve, thirteen, fourteen, fifteen, sixteen, seventeen,eighteen, nineteen, twenty or more loci are co-amplified. In someembodiments employing multiplex co-amplification, not all of the primerpairs comprise a high stability primer.

After amplification, the products from the PCR reactions can beanalyzed, resolved, and/or characterized by any of a variety of methodsknown in the art. For example, PCR reactions can be analyzed bydenaturing samples and separating using gel electrophoresis or acapillary electrophoresis protocol. The results from this can then allowone to determine the number of repeats of the STR sequence that arepresent.

Aspects of the present teachings may be further understood in light ofthe following examples, which should not be construed as limiting thescope of the present teachings in any way.

Example 1 Amplification of gDNA

This example describes how one can employ loopable primers for theamplification of a substantial portion of a genome.

First, one obtains, provides, or is provided a sample that includesgenomic DNA. One can then generally isolate the genomic DNA in thesample from various non-DNA impurities in the sample. Following this,one can add a loopable primer to the solution containing the gDNA. Theloopable primer can include a degenerate section and therefore actuallycomprise numerous individual primers, each having a different 3′ targetspecific sequence. The conditions of the reaction will be set so thatthe loopable primer can hybridize to the gDNA, while the loopable primeris in its looped conformation. The loopable primer is then extended toeventually form a double-extended loopable primer.

Following this, an amplification step can be performed with anamplification primer. The amplification primer includes a section thatis substantially identical in sequence to the universal region and,optionally the noncomplementary region (if present) in the originalloopable primer. Optionally, an amplification primer can also include asequence that is substantially identical to the second loop formingregion. PCR can then be performed on the solution, using thisamplification primer.

Following this, a digest is performed on the solution so that any singlestranded primers are eliminated. This can be achieved via exonuclease I.

Following this, the conditions of the solution are adjusted, ifnecessary, to allow the shorter double-extended loopable primers toself-hybridize.

Insert amplification primers are then added to the solution. The insertamplification primers can be degenerate primers or universal primers.

The amplified double-extended loopable primer can also be divided intoseparate containers (such as wells) and a specific insert amplificationprimer (or primer set) added to each container to allow amplification tooccur based on that specific insert amplification primer (or set).Numerous such insert amplification primers can be used in series orparallel in the separate containers. A PCR is performed on the solution(or more specifically for each solution) under conditions that allow theannealing and extension of the insert amplification primers, whilekeeping the conditions such that the double-extended loopable primer isself-hybridized.

The above steps will result in the amplification of the target nucleicacid sequence.

Example 2 Modification for Distinguishable Ends of the Product

This example provides an additional option for manipulating theamplified DNA for subsequent ease of use in various sequencingtechniques. Using Example 1 as the general template, one can add anadditional step, after the creation of the double-extend loopableprimer, to add a specific sequence on the tail of the nucleic acidsequence being amplified. In some embodiments, this tail sequence allowsone end of the nucleic acid sequence to have a specifically desirednucleic acid sequence, which can be advantageous in various sequencingmethods.

This specific tail sequence can be added through the use of a secondamplification primer that has a tail section that will not effectivelyhybridize to the double-extended loopable primer (or the complementthereof). Alternatively, the tail section can be added in a subsequentreaction, after an amplification of the double-extended loopable primer.

The addition of the specific tail sequence can be achieved before theformation of the self-hybridized structure, or during or after theamplification of the target nucleic acid sequence in the insert section(which is achieved in Example 1 via the insert amplification primers).

Example 3 Formation of Double-Extended Loopable Primers, Two DifferentLoopable Primers

This example demonstrates one embodiment in which RNA can be amplifiedby two loopable primers.

Loopable primers are added in excess to a solution that includes atarget sequence to be amplified. The loop section of the loopable primerinclude sequences of poly(T) (as the noncomplementary region) and auniversal region site in the loop. The sequences of the primers areshown in Table 1. The last four primers in Table 1 include two sets ofloopable primers, one having 6 and the other having 8 nucleic acids inthe 3′ target specific region.

TABLE 1 Primer Sequences UF-T10 GTCGACTGCGTGGAGTCGGCTTTTTTTTTT(SEQ ID NO: 1) UR-T10 TCATGATCCGTGGAGTCGGCTTTTTTTTTT (SEQ ID NO: 2)(N)8-T10-UP-RP TCATGATCCGTGGAGTCGGCTTTTTTTTTT GATCATGANNNNNNNN(SEQ ID NO: 3) (N)6-T10-UP-RP TCATGATCCGTGGAGTCGGCTTTTTTTTTTGATCATGANNNNNN (SEQ ID NO: 4) (N)8-T10-UP-FPGTCGACTGCGTGGAGTCGGCTTTTTTTTTT CAGTCGACNNNNNNNN (SEQ ID NO: 5)(N)6-T10-UP-FP GTCGACTGCGTGGAGTCGGCTTTTTTTTTT CAGTCGACNNNNNN(SEQ ID NO: 6)

Next, the double extended loopable primer are synthesized by the otherlooped primer. As will be appreciated by one of skill in the art, thiscan occur concurrently with the above process.

The length of the poly(T) (noncomplementarty region) and universalregion are long enough to form stable stem structure uponself-hybridization (as shown in FIG. 5), so that self-hybridizeddouble-extended loopable primers that only include short fragments oftarget DNA are not be further PCR amplified.

The amplification primers are then added to the solution and thedouble-extended loopable primers are then amplified by PCR. The cDNAsare amplified by 20 cycles of PCR by two amplification primers thatinclude universal regions (FP-T 10) and the noncomplementary region (seeTable 2 for specific protocols and conditions).

The result of the above steps is the amplification of thedouble-extended loopable primer, the shorter products of which can thenbe allowed to self-hybridize. The self-hybridized double-extendedloopable primers that include longer target nucleic acid sections (inwhich about 1 kb or more has been incorporated) have a larger insertsection that will allow subsequent insert amplification primers toanneal within the loop structure.

In an alternative example, following the amplification of thedouble-extended loopable primer, while the shorter double-extendedloopable primers can self-hybridize, the longer double extended loopableprimers do not self-hybridize. Self-hybridized structures are notamplified further; thus, selective amplification between short and longdouble-extended loopable primers can be achieved simply by the selectiveamplification of those double-extended loopable primers that are notself-hybridized.

In yet another alternative example, the selective amplification of thelonger double-extended loopable primer over the shorter double-extendedloopable primer occurs during the amplification of the double-extendedloopable primer. As the shorter double-extended loopable primers canself-hybridize, the longer double extended loopable primers do notself-hybridize. Self-hybridized structures are not amplified further;thus, selective amplification between short and long double-extendedloopable primers can be achieved simply by the selective amplificationof those double-extended loopable primers that are not self-hybridized.

TABLE 2 Stock Final 10x protocol Volume Concentration Concentrationmixture step 1 RT 10 10x cDNA Archiving Kit buffer 0.5 10 1 5 MMLV50u/ul 1 50 10   (10 u/ul) 10 100 mM dNTP 0.25 100 5  (100 mM/uL) 2.5(N)8-T10-UP-RP (20 uM) 0.25 20000 1000   (1 uM) 2.5 total RNA 10 ng/ulsamples 2 10 4 20 H2O 0.25 0 0 2.5 MgCl2 (25 mM) 0.75 25 3.75  (3.4 mM)7.5 total volume 5 (50 C. 1 sec-42 C. 20 sec-20 C. 30 sec) 30 cycles, 85C. 5 min step 2 extension and pre-PCR 10 2xUMM (No UNG) 2.5 2 1 25RT-template 1 0 0 (N)8-T10-UP-FP (20 uM) 0.5 20 2   (2 uM) 5 UF-T20 100uM 0.1 100 2   (2 uM) 1 UR-T20 100 uM 0.1 100 2   (2 uM) 1 AmpliTaqGold5 u/ul 0.25 5 0.25 (0.25 u/ul) 2.5 dNTP 100 mM 0.1 100 2   (2 mM) 1MgCl2 25 mM 0.2 25 2.5 total volume 5 40 95 C. 10 min (95 C. 1 sec-42 C.1 min) 10 cycles (95 C. 1 sec-65 C. 1 min) 10 cycles

While the above protocol can be used to amplify target nucleic acidsequences, the use of separate forward and reverse loopable primers cancomplicate the results. In light of this, a single degenerate loopableprimer was examined and the experiment and results are outlined inExample 4.

Example 4 Formation of Double-Extended Loopable Primers

This example demonstrates how a loopable primer (which included adegenerate 3′ target specific portion) was used for the amplification ofvarious target sequences (in the form of double extended loopableprimers). The various primers used (including the loopable primer) areshown in FIG. 8. The “8N-T10-RP” primer was the loopable primer sequencethat was employed. The repeat of “N” at the 3′ end denotes a degenerateend, representing all possible sequence combinations of A, T, G, and Cfor 8 nucleotides of sequence. Thus, this primer sequence represents 4⁸different primer sequences in this section of the loopable primer. Thetarget sample was CEPH gDNA (human, parts #4312660, Applied Biosystems).

The particular details of the protocol are outlined in Table 3. First,the loopable primer was added to the solution containing the targetsequence. The loopable primer hybridized to the target. The loopableprimer was then extended multiple times so that the amplified productsincluded both a universal region sequence and a universal regioncomplement (and therefore were double-extended loopable primers). Thespecific parameters performed for achieving this are outlined in Table3, step 1. Following this, the solution was treated with Exo I to digestrandom primers (outlined in Table 3, step 2). Following this, pre-PCRwas carried out on the solution using a single primer, UR-T10 (outlinedin Table 3, step 3).

TABLE 3 stock Final concentratoins cocentration Final Whole genomeAmplification volume (uL) (uM) (uM) cocentration step 1 extension andpre-PCR 10xPCR buffer II 1 10 1 DNA-template (95 C. 5 min pre-denature)2 0 0 N8-UR-T10 (100 uM) 2 100 20 (20 uM) AmpliTaq 5 u/ul 1 5 0.5 (0.5Unit/ul) dNTP 100 mM 0.5 100 5 (5 mM) MgCl2 25 mM 1.2 25 3 (3.0 mM) H2O2.3 total volume 10 95 C. 1 min (95 C. 15 sec-35 C. 4 min-65 C. 4 min)10 cycles step 2 PCR clean up with Exo I digestion of random primers 10ul above product + 2 ul ExoSAP 37 C. 15 min, 85 C. 5 min step 3 furtherextension and pre-PCR 10xPCR buffer II 2 10 1 step 2 products 12 0UR-T10 100 uM 2 100 10 (10 uM) dNTP 100 mM 0.5 100 2.5 (2.5 mM) MgCl2100 mM 1 25 1.25 (1.25 mM) AmpliTaq 5 u/ul 1 5 0.25 (0.25 u/ul) H2O 2.20 total volume 20 95 C. 1 min (95 C. 15 sec-65 C 4 min) 30x step 3product 20 ul + dH2O 80 ul = 100 ul (1:5 dilution)

The above protocol resulted in the selective amplification of a largeamount of target nucleic acid sequences in the double-extended loopableprimers. The results are displayed in FIG. 10, which is a gel on whichthe product from this Example was run. The results shown in the geldemonstrate that varying starting amounts of the genomic DNA (0.4-10ng), while resulting in various amounts of product, all displayedsignificant amplification (as shown by the strong bands at 2 and 10 ng).As will be appreciated by one of skill in the art, the target DNA wasamplified as part of the double extended loopable primer. The fact thatsignificant portions of the target DNA were amplified is demonstrated bythe relatively large size of the amplified product (larger than theprimers and significant amounts above 500 bp). This confirms that thisaspect of the technique functions as described herein. Additionally,FIG. 10 demonstrates the selective and effective amplification of largerfragments over smaller fragments. As can be observed in FIG. 10,significant amounts of amplification was demonstrated at the largerranges (the upper part of the gel, over and around 500 bp), furtherdemonstrating the effectiveness of this technique in selectivelyamplifying relatively large sections.

The increase in amplification ability of the above example isquantitated in some of the examples below; however, it is noted that thegeneral technique can amplify an input nucleic acid sequence by about3000 fold (input of 10 ng and output of 30 micrograms) to severalhundred thousand fold. In contrast to this, other amplificationtechniques available in the art result in only a 30 fold amplification.

Example 5 Distinguishable Primer Ends

This example demonstrates one option for adding a different primer tailonto the double-extended loopable primer. To the products produced inStep 3 in Example 4, an additional amplification primer was added(SEQ1-U-T10) as well as a primer with a second tail end, but wasotherwise similar to the amplification primer (e.g., SEQ2-U-T10). Thesolution was then PCR amplified as shown in Table 4.

TABLE 4 stock Final concentratoins cocentration Final Two primer PCR forSequencing application volume (uL) (uM) (uM) cocentration 10xPCR bufferII 2 10 1 step 3 products (1:5 dilution) 2 0 SEQ1-U-T10 100 uM 1 100 5(5 uM) SEQ2-U-T10 100 uM 1 100 5 (5 uM) dNTP 100 mM 0.5 100 2.5 (2.5 mM)MgCl2 100 mM 1 25 1.25 (1.25 mM) AmpliTaq 5 u/ul 1 5 0.25 (0.25 u/ul)H2O 2.5 0 total volume 11 95 C. 1 min (95 C. 15 sec-65 C. 4 min) 15x

This process added a different sequence (the 5′ end of UR-T10) to oneend of the amplified sequence in order to allow for various sequencingtechniques to be employed on the amplified sequence.

Example 6 Insert Section Amplification

This example presents the results of a study that examined theeffectiveness of the techniques discussed in Example 4, when theadditional step of the loop amplification was performed. Furthermore,this example also provides a demonstration of the additional step of theactual insert section amplification step, via a TAQMAN® assay.

In order to test the effectiveness of the amplification of the targetnucleic acid sequences and the ability of the insert amplification stepto function as described above, the presence of a target sequence in theamplified target nucleic acid sequences (the double-extended loopableprimer) was examined via a TAQMAN® gene expression assay for Rnase P.The details of the Rnase P protocol are shown in Tables 5.

TABLE 5 stock Rnase P assay volume (uL) concentratoins 2x UMM Mix (NOUNG) 5  2x step 3 products (1:5 dilution) 2 20x RNase P Mix of primersand TaqMan 0.5 20x probe H2O 2.5 total volume 10 95 C. 1 min (95 C. 15sec-60 C. 1 min) 40x

Table 6 summarizes the results between the experimental data and themock experiment controls. A comparison of the amplified and mocked (keepin −20 C) reactions was made to determine effectiveness of generaltechnique.

TABLE 6 10 ng CEPH DNA inputs Amplifcation Ct of Ct of AmplifiedAmplified folds Rnase P Rnase P NTC NTC DNA ug DNA ug UR-T10 19.31 19.2435.82 35.81 29.03 30.47 mock UR-T10 30.81 30.42 35.66 35.89 0.01 0.01Amplification 2902 2323 1 1 folds

As shown in Table 6, the results from the RNase P assay demonstratedthat the amplification fold of the above steps (Example 4 and thepresent example) was between 2902-2323 for a single primer PCR in 30cycles. The yield noted above was calculated as follows:

Amplification fold=2̂(Ct of mock−Ct of UR-T10)=2̂(30.81−19.31)=2902.

The yield of DNA at Step #3=amplification fold×gDNA input=2902*10ng=29.02 μg. Alternatively, using the standard curve to determine yieldsresults in the following:

Yield of DNA at Step #3=10 ng×50(dilution factor)×2̂(Ct of 10 ngstandard−Ct of UR-T10)=10×50×2̂(25.17−19.31)=29030 ng=29.03 μg.

The Ct of Rnase P for 5 ng was 26.15, for 10 ng was 25.17 and for 20 ngwas 24.08. As only 2 μL of the 100 μL produced in step #3 was used forthe RNase P quantification, there was a 50-fold dilution factor.Adjusting for this, given a 10 ng CEPH gDNA input at step 1, thetechnique resulted in 29-30 μg of amplified DNA fragments.

In addition to the quantitative results demonstrated above, FIG. 9further demonstrates the ability of some of the various embodiments toachieve various desired amounts of amplification. FIG. 9 demonstratesthat the technique displayed a desired decrease in cycle threshold asincreasing amounts of starting target DNA are used (from 0 to 10 ng ofNA12961 gDNA (Coriell DNA purchased from Coriell Institute). As such, itis clear that the technique appears to function as noted herein.

Example 7 Effectiveness of Exo I Digest, and the Effectiveness ofVariously Sized 3′ Target-Specific Portion Regions in the LoopablePrimer

The present example demonstrates the results of modifying variousvariables in Example 4. Specifically, the experiment in Example 4 wasrepeated with and without the Exo I digest and using variously sized 3′target specific regions (8-12 nucleic acids of degenerate sequence). Theresults for these varied conditions are presented in FIG. 11 (with noExo I digest) and FIG. 12 (with an Exo I digest).

The smears in the lanes in the gel in FIG. 11 demonstrate that, for amethod similar to that described in Example 4 (except that no Exo Idigest step was performed), selective amplification of relatively largesized fragments of the target nucleic acid sequence occurred for 8, 9,10, 11, and 12 mer sized 3′ target-specific portion (e.g., degenerate)regions on the looped primer. This is displayed by the high amount ofproduct distributed in the upper section of the experimental lanes(indicated by “20”) compared to the negative control lanes (indicated by“0”). It is clear from the results in FIG. 11 that a variety of lengthsof 3′ target-specific portions or degenerate regions will work on theloopable primer.

The results shown in the gel in FIG. 12, which included the Exo Idigestion step (step 2) in Example 4, demonstrate that even higheramounts of product can be obtained if the Exo I digest step is included(as shown by the amount and distribution of material in the experimentallanes (20 ng) instead of the control lanes (0 ng) compared to theresults in FIG. 11).

Example 8 Exo I Treatment Post WGA Procedure

This example demonstrates one embodiment in which the cleaning step(e.g., Exo I treatment) is performed later in the procedure (after the“further extension and pre-PCR”). The specifics of the protocol areoutlined in Table 7.

TABLE 7 stock Final concentratoins cocentration Final Whole genomeAmplification volumes (uL) (uM) (uM) cocentration step 1 extension andpre-PCR 10xPCR buffer II 2 10 1 DNA-template 4 0 0 N8-UR-T10 (100 uM) 2100 10 (10 uM) AmpliTaq 5 u/ul 4 5 1 (1 Unit/ul) dNTP 100 mM 1 100 5 (5mM) MgCl2 25 mM 2.4 25 3 (3. 0 mM) H2O 4.6 total volume 20 95 C. 5 min(95 C. 30 sec-35 C. 2 min-65 C. 2 min) 20 cycles step 2 furtherextension and pre-PCR 10xPCR buffer II 4 10 1 above reagent 20 0 UR-T10100 uM 4 100 10 (10 uM) dNTP 100 mM 1 100 2.5 (2.5 mM) MgCl2 25 mM 2.425 1.5 (1.5 mM) AmpliTaq 5 u/ul 2.6 5 0.325 (0.325 u/ul) H2O 6 0 totalvolume 40 95 C. 1 min (95 C. 30 sec-65 C. 1 min-72 C. 2 min) 30x step 3PCR clean up 10 ul above product + 2 ul ExoSAP 37 C. 15 min, 85 C. 5 minabove 10 ul product load on the gel

The results of these initial rounds of amplification are shown in FIG.13. As shown in the gel in FIG. 13, substantially large sections of thetarget nucleic acid were amplified (as shown by the relatively highweight of the amplified product, with most of the smear falling between200 bp to 2 kb in the appropriate lanes). Additionally, these resultsfurther demonstrate that even for the smaller amounts of initial sample,an appropriately scaled amount of final product can be achieved (e.g., 4pg of starting material resulted in a correspondingly smaller amount offinal product than 40 pg and 40 pg resulted in a correspondingly smalleramount than 400, etc.). These results further demonstrate that the useof these loopable primers can readily result in highly efficientamplification of very low starting samples (e.g., 4 pg shows up on thegel) with a desired sized amplification product (e.g., between 200 bpand 2 kb and a large amount of amplification around the 400 to 800 bprange).

Following the Exo I nuclease digestion, insert amplification primers forRNase P were added in a TAQMAN® assay in order to demonstrate theadditional step of insert amplification and to demonstrate theamplification abilities of the technique. The results are shown in Table8.

TABLE 8 Rnase N8- N8- N8- N8- P Assay T10-RP T10-RP T10-RP T10-RP CEPHreal real mocked mocked Amplification gDNA (Ct) (SD) (Ct) (SD) Folds SD40 ng 17.60 0.03 29.08 0.38 2904 816  4 ng 17.05 0.11 32.23 0.42 3823713558 400 pg  16.16 0.09 35.54 1.33 812717 624835 40 pg 17.97 0.04 37.021.37 675933 569503  4 pg 24.23 0.18 36.84 0.11 6289 303 NTC 37.17 0.4440.00 0.00 7 2

As shown in amplification results in Table 8, the use of the Exo Inuclease cleaning step following the extension and pre-PCR stepsresulted in a substantial increase in the amplification fold of thetarget nucleic acid sequence. As shown above, using this embodimentresulted in more than an 800,000 fold amplification when starting with400 pg of target nucleic acid.

It is noted that the apparent increase in amplification fold (from 40 ngto 400 pg) is likely due to the higher starting amounts already beingsaturating (as they all have a similar Ct). Similarly, it is noted thatthe lower amplification amounts (from the 40 pg to 4 pg) is likely dueto the relatively higher amount of intrinsic variation that can occurwhen such small starting samples are used.

Example 9 Varied Number of PCR Cycles in Step 2

This example demonstrates how varying the number of cycles in step 2 ofthe PCR protocol (in Example 8) can produce various results that areconsistent with the teachings herein. The example demonstrates thatvarying the number of cycles can improve the final yield of theprotocol. Additionally, the example demonstrates that varying the numberof cycles can also maintain or result in a better dose response. Theimpact of varying the number of cycles in step 2 was examined for theprotocol disclosed in Example 8, including 14, 20, 25, and 30 cycles.The results are presented in FIG. 14 and Tables 9 and 10.

As can be observed in the gel depicted in FIG. 14, 25 cycles in step 2resulted in observable amplification for 40 pg, 400 pg, 4 ng, and 40 ng.Additionally, the amplification at these ranges did not saturate; thus,for this range of concentration of target nucleic acid sequence,amplification can be readily achieved while maintaining appropriaterelative concentrations between various target nucleic acid sequences.Furthermore, one can observe that, while there is some apparentsaturation for 30 cycles, amplification was appropriate and maintainedits relative distribution for at least the 40 pg to 400 pg range.

TABLE 9 Rnase P Assay N8-T10-RP CEPH step 2 × 14 N8-T10-RP N8-T10-RPN8-T10-RP gDNA (Ct) SD step 2 × 20 (Ct) SD  40 ng 26.98 0.22 22.41 0.11 4 ng 27.98 0.32 23.00 0.13 400 pg 29.47 0.22 24.94 0.11  40 pg 35.590.01 29.26 0.03  4 pg 37.12 0.82 36.13 0.73 NTC 38.81 1.68 39.62 0.53

TABLE 10 N8-T10-RP N8-T10-RP Rnase P Assay step 2 × 25 N8-T10-RP step 2× 30 N8-T10-RP CEPH gDNA (Ct) SD (Ct) SD  40 ng 18.61 0.06 15.72 0.37  4ng 18.65 0.36 15.63 0.08 400 pg 20.10 0.06 15.15 0.22  40 pg 34.24 0.4517.84 0.11  4 pg 34.01 0.30 34.58 0.38 NTC 34.15 0.20 33.92 0.36

As can be observed in the results presented in Tables 9 and 10,increasing the number of cycles resulted in a larger increase in theamount of final product (noted by the decrease in the Ct). Additionally,the results generally demonstrate that, by using varying cycle numbers,one can amplify varying amounts of initial target nucleic acid sequence,while maintaining the relative ratios of the various target nucleic acidsequences. Furthermore, the above results generally provide guidance asto what initial cycle number should be used when amplifying the variousranges of initial target nucleic acid sequence. Of course, these numberscan be routinely optimized with the disclosure presented herein.

Example 10 RNA Amplification

This example demonstrates one application for some of the presentembodiments for RNA amplification. The protocol for the first 4 steps(prior to the insert amplification) is generally outlined in Table 11.

TABLE 11 stock Final concentratoins cocentration Final Whole genomeAmplification (uM) (uM) cocentration step 1 Random primer RT 10x cDNAArchiving Kit buffer 0.50 10 1 1x MMLV 50 u/ul 0.50 50 5 5 U/uL 100 mMdNTP 0.25 100 5 (5 mM) 10x random primers (100 uM) 0.50 10 10 (10 uM) HLtotal RNA 40 ng-4 pg 2.00 MgCl2 25 mM 0.60 25 3 3.0 mM/uL H2O 0.65 totalvolume 5.00 RT 25 C. 10 min, 37 C. 120 min, 85 C. 5 min step 2 extensionand pre-PCR volumes (uL) 10xPCR buffer II 2 10 1 1x RT products clean up6 0 0 N8-UR-T10 (100 uM) 2 100 10 (10 uM) AmpliTaq 5 u/ul 4 5 1 (1Unit/ul) dNTP 100 mM 1 100 5 (5 mM) MgCl2 25 mM 2.4 25 3 (3.0 mM) H2O2.6 0 0 total volume 20 95 C. 1 min (95 C. 30 sec-35 C. 2 min-65 C. 2min) 20 cycles step 3 further extension and pre-PCR 10xPCR buffer II 410 1 1x above reagent 20 0 UR-T10 100 uM 4 100 10 (10 uM) dNTP 100 mM 1100 2.5 (2.5 mM) MgCl2 25 mM 2.4 25 1.5 (1.5 mM) AmpliTaq 5 u/ul 4 5 0.5(0.5 u/ul) H2O 4.6 0 total volume 40 95 C. 1 min (95 C. 30 sec-65 C. 1min-72 C. 2 min) 30x step 4 PCR clean up 10 ul above product + 2 ulExoSAP 37 C. 15 min, 85 C. 5 min above 10 ul product load on the gel or2 uL to run RNAse P TaqMan assay

As shown in Table 11, when one wishes to amplify RNA instead of gDNA,one can add an initial step (step 1) for reverse transcription. In step1 of the present example, random primer reverse transcription wasinitially performed on the target sample. Following this, a similar setof protocols (as in Example 8) was performed on the starting sample. Theresults are displayed in FIG. 15. As shown in FIG. 15, the desiredsmears in the appropriate lanes demonstrate the expected amplificationof the relatively large sections of target nucleic acid sequence(incorporated in the double-extended loopable primer).

As in some of the above examples, the amplified product (double-extendedloopable primer) was then used for further, selective amplification viathe insert amplification primers for RNase P, via a TAQMAN® assay forRNase P. The results from this experiment are displayed in Table 12.

TABLE 12 N8-T10-RP N8-T10-RP N8-T10-RP N8-T10-RP Rnase P Assay Ct valuesSD Ct values SD Human Lung no Exo after no Exo after Exo after Exo afterRNA step 1 step 1 step 1 step 1  40 ng 15.08 0.08 15.37 0.09  4 ng 18.100.03 23.10 0.16 400 pg 17.41 0.01 25.02 0.01  40 pg 24.43 0.08 28.820.25  4 pg 27.73 0.46 33.03 0.18 NTC 33.63 0.03 37.32 3.80

As demonstrated in the results above, the technique clearly functionedfor RNA amplification. Furthermore, as shown in the second column ofTable 12, even starting amounts as low as 4 pg resulted in significantamounts of final product (e.g., under 30 Ct).

Additionally, the results in Table 12 further presents data thatcompares the impact of including an EXO I digestion step after step 1 ornot. As can be seen from the data, a substantial amount of amplificationoccurred with or without an Exo I step after step 1. Surprisingly, itwas found that adding the Exo I step, after the first step (step 1)decreased the resulting amount of product.

In light of the above, it appears that the EXO I step can be especiallybeneficial when used following the single primer amplification. This wassurprising because the use of the EXO I step at an earlier stage(following the first step) was not as effective.

Example 11 Insert Amplification—Primer Pools

As will be appreciated by one of skill in the art, in many of theembodiments described above, insert amplification can be achieved basedon knowing which sequence was (or should be) contained within the loop,such as RNase P. In situations in which the target within the insertsection is not initially known, such as when an entire genome is beingamplified, the protocol can be varied slightly to take this variableinto account. For example, indiscriminant primers could be used.Alternatively, and as described in this example, numerous primers can betested or used on the amplified sample.

Following any of the above initial amplification procedures (e.g., at apoint following the formation of the double-extended loopable primer,but prior to the use of an insert amplification primer) one can dividethe amplified product into numerous subsamples. Each subsample willsimply be a fraction of the amplified product, and thus can include arepresentative (e.g., proportionate and substantially complete)distribution of the various double-extended loopable primers. Eachsubsample can be placed in a separate well, to which a specific known,or knowable, insert amplification primer, or primers, can be added.Following this, an amplification step can be performed in each of thewells. This will allow for the amplification of the looped section ofthe self-hybridized double-extended loopable primer. These amplifiedsequences can then be detected, such as by sequencing.

Example 12 STR Amplification

The present example demonstrates how one can use the methods and primersdescribed herein to amplify a STR locus of interest.

At least one loopable primer, having a 3′ target specific region thatwill bind near a locus to be examined, is combined with a sample thatincludes a target nucleic acid sequence. The 3′ target specific regioncan be selected so that it binds near at least one of the followingloci: TH01, TPOX, CSF1PO, vWA, FGA, D3S1358, D5S818, D7S820, D13S317,D16S539, D8S1179, D18S51, D21S11, D2S1338, D3S1539, D4S2368, D9S930,D10S1239, D14S118, D14S548, D14S562, D16S490, D16S753, D17S1298,D17S1299, D19S253, D19S433, D20S481, D22S683, HUMCSF1PO, HUMTPOX,HUMTH01, HUMF13AO1, HUMBFXIII, HUMLIPOL, HUMvWFA31, Amelogenin, D12s391,D6S1043, SE33, or any combination thereof. The amplification outlined inany of the above examples or embodiments can be performed, therebyresulting in the amplification of the relevant locus.

Example 13 STR Amplification

The present example demonstrates how one can use the methods and primersdescribed herein to amplify a STR locus of interest.

At least one loopable primer, having a 3′ target specific region thatcomprises a degenerate region, is combined with a sample that includes atarget nucleic acid sequence. The loopable primer is used to amplify thetarget nucleic acid sequence as provided in any of the above examples.However, once the double extended loopable primer is created, the insertamplification primers that are used are selected so that the insertamplification primers bind near at least one of the following loci:TH01, TPOX, CSF1PO, vWA, FGA, D3S1358, D5S818, D7S820, D13S317, D16S539,D8S1179, D18S51, D21S11, D2S1338, D3S1539, D4S2368, D9S930, D10S1239,D14S118, D14S548, D14S562, D16S490, D16S753, D17S1298, D17S1299,D19S253, D19S433, D20S481, D22S683, HUMCSF1PO, HUMTPOX, HUMTH01,HUMF13AO1, HUMBFXIII, HUMLIPOL, HUMvWFA31, Amelogenin, D12s391, D6S1043,and SE33. This will then allow for the amplification of the STR at therelevant locus.

As will be appreciated by one of skill in the art, numerous insertamplification primers can be used for the above processing, e.g., 2-10,10-50, 50-100, 100-1000, 1000-10,000, 10,000-30,000, 30,000-40,000,40,000-50,000, 50,000-100,000, or more primers. Each can be used in aseparate well with a representative portion of the amplified targetnucleic acid sequence. As will be appreciated by one of skill in theart, during the amplification, the conditions should be such that thedouble-extended loopable primer is self-hybridized, resulting in theselective amplification of the initially amplified products of thedesired size.

The above results clearly establish that the presently disclosedprocesses can be effective in selectively amplifying usefully sizedfragments throughout relatively long stretches of gDNA from a targetsample. While the above embodiments have been described in terms of aloopable primer, in other embodiments, the initial primer can be linearor need not be loopable (as long as there is a universal region that isplaced on one end and its complement is placed on the other end of asection of nucleic acid to be amplified). Thus, in some embodiments, anyor every one of the above embodiments can be used with a linear primerinstead of a loopable primer.

Furthermore, in some embodiments, the amount of amplification is,compared to the current state of the art, very high (approximately 3000fold to over hundreds of thousands fold), while still amplifying thelarger fragments. This is in contrast to previous attempts atamplification using random primers that appeared to generally reachlower levels of amplification. (See, e.g., Zhang et al., PNAS, vol. 89,5847-5851, (1992), approximately 30 fold; and Genomeplex® Whole GenomeAmplification (WGA) Kit by Sigma-Aldrich, discussed on the world wideweb atbiocompare.com/review/769/Genomeplex-Whole-Genome-Amplification-(WGA)-Kit-by-Sigma-Aldrich.html, discussing 3000 fold). Additionally, as shown above, theamplification ability can be enhanced through the use of an Exo Idigestion step, although this is clearly not required. It is believedthat these data demonstrate that 3′ target-specific portions (e.g.,degenerate regions) of 7-15 nucleic acids in length will work for someembodiments. Additionally, in some embodiments these relatively largeincreases in amplification are achieved while still maintaining somedegree of dose response during the amplification. For example, in someembodiments, relatively small amounts of one species to be amplifiedwill still be a relatively small percent of the amplified product(although it could have been amplified, e.g., 100-1,000,000 times).

In this disclosure, the use of the singular can include the pluralunless specifically stated otherwise or unless, as will be understood byone of skill in the art in light of the present disclosure, the singularis the only functional embodiment. Thus, for example, “a” can mean morethan one, and “one embodiment” can mean that the description applies tomultiple embodiments. The phrase “and/or” denotes a shorthand way ofindicating that the specific combination is contemplated in combinationand, separately, in the alternative.

The section headings used herein are for organizational purposes onlyand are not to be construed as limiting the described subject matter inany way.

It will be appreciated that there is an implied “about” prior to thetemperatures, concentrations, times, etc. discussed in the presentteachings, such that slight and insubstantial deviations are within thescope of the present teachings herein. For example, “a primer” meansthat more than one primer can, but need not, be present; for example butwithout limitation, one or more copies of a particular primer species,as well as one or more versions of a particular primer type, for examplebut not limited to, a multiplicity of different loopable primers. Also,the use of “comprise”, “comprises”, “comprising”, “contain”, “contains”,“containing”, “include”, “includes”, and “including” are not intended tobe limiting. It is to be understood that both the foregoing generaldescription and detailed description are exemplary and explanatory onlyand are not restrictive of the invention.

Unless specifically noted in the above specification, embodiments in theabove specification that recite “comprising” various components are alsocontemplated as “consisting of” or “consisting essentially of” therecited components; embodiments in the specification that recite“consisting of” various components are also contemplated as “comprising”or “consisting essentially of” the recited components; and embodimentsin the specification that recite “consisting essentially of” variouscomponents are also contemplated as “consisting of” or “comprising” therecited components (this interchangeability does not apply to the use ofthese terms in the claims).

INCORPORATION BY REFERENCE

All references cited herein, including patents, patent applications,papers, text books, and the like, and the references cited therein, tothe extent that they are not already, are hereby incorporated byreference in their entirety. In the event that one or more of theincorporated literature and similar materials differs from orcontradicts this application; including but not limited to definedterms, term usage, described techniques, or the like, this applicationcontrols.

EQUIVALENTS

The foregoing description and Examples detail certain preferredembodiments of the invention and describes the best mode contemplated bythe inventors. It will be appreciated, however, that no matter howdetailed the foregoing may appear in text, the invention may bepracticed in many ways and the invention should be construed inaccordance with the appended claims and any equivalents thereof.

1. A loopable primer comprising: a 3′ target specific region; a firstloop forming region; a universal region; and a second loop formingregion, wherein the first loop forming region and the second loopforming region are configured to hybridize to each other to form a stemand a loop, wherein the universal region is located between the firstand second loop forming regions, wherein the stem and the loop, whenformed, are configured to allow the 3′ target specific region tohybridize to a target nucleic acid without the remainder of the loopableprimer annealing to the target nucleic acid, and wherein the universalregion is configured to form a self-hybridized structure on subsequentamplifications.
 2. The loopable primer of claim 1, wherein the 3′ targetspecific region comprises a degenerate sequence.
 3. The loopable primerof claim 1, further comprising a noncomplementary region located in thenucleic acid sequence between the first universal region and the secondloop forming region.
 4. The loopable primer of claim 1, furthercomprising a foreign insert section of DNA.
 5. The loopable primer ofclaim 4, wherein the foreign insert section of DNA is longer than thelength of the 3′ target specific region.
 6. The loopable primer of claim1, wherein the 3′ target specific region comprises a nucleotide sequencethat can amplify a desired short tandem repeat.
 7. The loopable primerof claim 1, wherein the 3′ target specific region comprises a nucleotidesequence that can amplify a locus selected from one or more of the groupconsisting of: TH01, TPOX, CSF1PO, vWA, FGA, D3S1358, D5S818, D7S820,D13S317, D16S539, D8S1179, D18S51, D21S11, D2S1338, D3S1539, D4S2368,D9S930, D10S1239, D14S118, D14S548, D14S562, D16S490, D16S753, D17S1298,D17S1299, D19S253, D19S433, D20S481, D22S683, HUMCSF1PO, HUMTPOX,HUMTH01, HUMF13AO1, HUMBFXIII, HUMLIPOL, HUMvWFA31, Amelogenin, D12s391,D6S1043, SE33, or any combination thereof.
 8. The loopable primer ofclaim 3, wherein the noncomplementary region comprises 4-15 thyminenucleotides.
 9. The loopable primer of claim 8, wherein thenoncomplementary region consists essentially of 7-15 thyminenucleotides.
 10. The self-hybridizable DNA structure in a PCRamplification mixture, said self-hybridizable DNA sequence comprising: afirst loop forming region; a universal region connected to the firstloop forming region; a second loop forming region connected to theuniversal region, wherein the first loop forming region and the secondloop forming region are complementary to each other; a first 3′ targetspecific region connected to the second loop forming region; a sequencethat is complementary to a second 3′ target specific region, wherein thesequence that is complementary to the second 3′ target specific regionis part of a same nucleic strand as the first 3′ target specific region;a sequence that is complementary to the second loop forming region,wherein the sequence that is complementary to the second loop formingregion is connected to the sequence that is complementary to the second3′ target specific region; a sequence that is complementary to theuniversal region, wherein the sequence that is complementary to theuniversal region is connected to the sequence that is complementary tothe second loop forming region; and a sequence that is complementary tothe first loop forming region, wherein the sequence that iscomplementary to the first loop forming region is connected to thesequence that is complementary to the universal region, wherein theself-hybridizable DNA structure is configured to form a stem and a loopstructure, wherein the stem is formed by hybridization of the sequencecomprising the first loop forming region, the universal region and thesecond loop forming region to the comprising their respectivecomplementary sequences.
 11. The self-hybridized DNA structure of claim10, wherein there is no cDNA located within or between the 3′ targetspecific region and the sequence that is complementary to the second 3′target specific region.
 12. The self-hybridized DNA structure of claim10, wherein the amount of cDNA located between the 3′ target specificregion and the sequence that is complementary to the second 3′ targetspecific region is less than 500 base pairs.
 13. The self-hybridized DNAstructure of claim 10, wherein the amount of cDNA located between the 3′target specific region and the sequence that is complementary to thesecond 3′ target specific region is less than 100 base pairs.
 14. Theself-hybridized DNA structure of claim 10, wherein the amount of cDNAlocated between the 3′ target specific region and the sequence that iscomplementary to the second 3′ target specific region is less than 50base pairs. 15-45. (canceled)
 46. A loopable primer comprising: a 3′target specific region; a first loop forming region; a universal region;a noncomplementary region; and a second loop forming region, wherein thefirst loop forming region and the second loop forming region areconfigured to hybridize to each other to form a stem and a loop, whereinthe universal region is located between the first and second loopforming regions, wherein the noncomplementary region is located betweenthe first and second loop forming regions, wherein the stem and theloop, when formed, are configured to allow the 3′ target specific regionto hybridize to a target nucleic acid without the remainder of theloopable primer annealing to the target nucleic acid, and wherein theuniversal region is configured so that a sequence associated with atarget sequence that has been amplified by the loopable primer can forma self-hybridized structure comprising the universal region, thenoncomplementary region, the first loop forming region, and the secondloop forming region on subsequent amplifications, wherein said loopableprimer is created by deliberately selecting the sequence of the firstloop forming region so that it hybridizes to the second loop formingregion, and wherein said loopable primer is created by deliberatelyselecting a universal region.
 47. The loopable primer of claim 2 whereinthe 3′ target specific region comprises a degenerate end.
 48. Theloopable primer of claim 1 wherein the 3′ target specific regioncomprises a random region.
 49. The loopable primer of claim 48 whereinthe 3′ target specific region is a random region.